MXPA96005967A - Dual dosing procedure for the reduction of pollutant emissions, control of combustion and increase of thermal efficiency in steam generators or ovens using residual fuels - Google Patents

Abstract

The present invention relates to a dual dosing process of additives for the reduction of polluting emissions, combustion control and increase of thermal efficiency in steam generators or furnaces that use residual fuels comprising: The combustion of fuel in the presence of a first quantity of additive containing Mg, Mn, compounds or combinations of said elements, the transportation of the combustion gases through the covective zone to a zone of lower temperature, and the simultaneous injection into the combustion gases of an additional quantity of additive based on magnesium, magnesium compounds or combinations of

Description

DUAL DOSING PROCEDURE FOR THE REDUCTION OF POLLUTANT EMISSIONS, CONTROL OF COMBUSTION AND INCREASE OF THERMAL EFFICIENCY IN VAPOR GENERATORS OR OVENS USING RESIDUAL FUELS.

DESCRIPTION OF THE INVENTION The present invention defines a method for improving thermal efficiency in a steam generator or furnace, while minimizing acid corrosion in the cold zone and improving the problem of acid emissions to the atmosphere, total suspended particles, and visual opacity. The problems of incomplete combustion, corrosion in the high and low temperature zones, acid emissions, total suspended particles and high visual opacity are problems potentially associated with the burning of fuel with a high content of impurities (mainly Na, V, Ni and Sulfur). Since the residual fuels (mainly fuel oil) began to be used in steam generators and furnaces, the aforementioned problems have arisen, which have a negative impact on the availability and efficiency of boilers and furnaces, in addition to the severe ecological impact so commented in recent years, and that have forced the various environmental protection agencies to issue ever stricter standards. Many efforts have been made to control one or several of these problems, among which stand out the operation of the units at low levels of excess air, redesign of the boilers, modification of their operating conditions and even the excessive maintenance thereof, as well as the application of additives. Various products have been tested for this purpose, mainly additives based on Magnesium and Manganese injected into the fuel, (known as pre-flame additives or front additive). However, there are potential problems with the injection of these additives mainly associated with overdosing thereof in order to achieve corrosion control in the cold zone. When large amounts of additives are used in co-butane oil based on Magnesium and / or Manganese, they cause excessive fouling inside the boiler, which makes them undesirable from the operational point of view. On the other hand, the additives themselves are expensive and, if used in large quantities, the cost of the treatment may be inaccessible and / or prohibitive from the economic point of view. It has also been observed that the Mg-based front additives are unable to provide adequate protection against corrosion and clogging by acid condensation in the cold areas of the boilers (air pre-heaters, ducts, chimneys). This has led to the use of an air preheating system, (by means of steam coils), before the combustion air reaches the regenerative air preheater in order to maintain the temperature of the metal surfaces of the air preheater. regenerative gases exposed above the dew point of sulfuric acid. This affects the efficiency of the boiler when obtaining a higher temperature of exhaust gases and the use of a percentage of the steam generated to heat the air instead of using it to produce energy. The impact that has on the efficiency of the boiler comes to represent a fuel oil consumption greater by 2 to 3% than would be consumed with closed snakes.

Objectives of the Invention The objectives of the present invention are the following: 1. - Improve the environmental effects of combustion by reducing the S03 in the chimney, total suspended particles and visual opacity, 2. - To fight corrosion and clogging in air preheater by means of the effective neutralization of condensed S03 as H2S04. 3.- Carry out the above through the use of an optimal amount of additives, improving the cost-benefit of the same. 4.- Improve thermal efficiency through the elimination of air-steam heating coils. 5.- Maintain the results offered by the front additives for the high temperature zone (superheater, hearth, reheater). 6.- Provide technology for the process of dosage of additives, which is adaptable to any existing installation or plant, for example in thermoelectric plants, and easy to install.

DESCRIPTION OF THE INVENTION The present invention refers to a dual dosage process of additives for the reduction of polluting emissions, combustion control and increase of thermal efficiency in steam generators or furnaces that use residual fuels, which consists of the following stages: A) The combustion of the fuel in the presence of a first quantity of additive containing magnesium, manganese, compounds based on these elements or the combination thereof; B) The transportation of these combustion gases through the convective zone, (superheaters, reheaters, convection pipes, etc.), to a zone of lower temperature, (regenerative air pre-heater, economizer, etc.). C) The simultaneous injection in the combustion gases of an additional quantity of additive based on magnesium, magnesium compounds or the combination of these. During the indicated procedure the fuel is burned in a boiler or furnace, and its gases are transported through the zone of superheaters (high temperature) to the area of economizers and air preheaters (low temperature) and expelled from it through the chimney. Optionally or preferentially, the method of the invention can be carried out according to the following modalities: a) The additive of step C) is applied in the low temperature zone, which is between 90 and 550 ° C. b) The additive of step C) is at least in a molar ratio of MgO to S03 of between 1: 1 and 4: 1. c) The application of the additives covers the operational variations that could generate greater S03 and comply with an effective neutralization of the condensed acid. d) The additive of part A) comprises only magnesium-containing substances, magnesium-derived compounds or a combination thereof. e) The additive of step A) comprises only substances containing manganese, manganese compounds, or a combination thereof. f) The additive of step A) is in a molar ratio of Mg: V of between 0.25: 1 and 1: 1. g) The additive of part A) is in a molar ratio of Mn: V between 0.25: 1 and 1: 1. h) During the process a portion of the combustion gases are recirculated to the combustion zone and in which a component of a substance that may consist of magnesium, magnesium compounds or a combination thereof is applied to the posterior zone of this recirculation of gases.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic of a conventional steam generator and its parts susceptible to high and low temperature corrosion. Figure 2 is a diagram of a steam generator in which the combined application of two additives according to the invention is observed DETAILED DESCRIPTION OF THE DRAWINGS While this invention is susceptible to having modalities in many forms, it is shown in the drawings, and only the specific modalities thereof will be described in detail, with the understanding that the following discussion should be considered as an exemplification of the principles of the invention and not intended to limit the invention to the specific embodiments illustrated. Figure 1 is a diagram of a conventional steam generator, and its parts, susceptible to corrosion of high and low temperature, which consists of a furnace (1), a JL reheater (2), an economizer (3), an air preheater (4) a chimney inlet (5) and a fan (5a), in which the dual dosing process of the invention can be carried out. Figure 2 is a graphical representation of the dual dosing process in the typical conventional boiler of Figure 1 without gas recirculation, in which first the fuel oil is injected into the line of burners, not shown, from where it passes to the oven (1) or combustion zone, where it is mixed with air, which has been previously heated.

In said furnace (1) combustion is carried out, and the heat energy released is transmitted to the bank of tubes located in the walls of the home, not shown, converting the water to steam. Subsequently the combustion gases pass to a convection zone that is comprised of a group of superheater and superheater tubes (2), and when they reach this zone the gases have decreased their temperature from 1300-1500 ° C to 430-480 ° C , passing the combustion products to the area of the economizers (3), where the boiler feed water is preheated, if it has that part. Then the combustion products flow through the gas pipeline at a temperature of 310 to 400 ° C until reaching the regenerative air preheater (4), whose function is to transfer the heat of the gases to the air for combustion in order to to increase its efficiency. Subsequently, the temperature of the combustion products reaches approximately 150 ° C, and these gases are emitted into the atmosphere through the chimney (5), close to the fan (5a). At this point the application of the dual dosage of the additives of the invention is observed, where before burners, on the fuel oil line a frontal additive based on Magnesium and Manganese (6) is injected to modify the characteristics of the tanks and improve fuel combustion. Finally, as the temperature of the gases decreases and the condensation of acidic products of combustion occurs, an additive based on Magnesium (7) is injected before the air preheater (4) in order to neutralize the acid condensers. DETAILED DESCRIPTION OF THE INVENTION The present invention involves the presence of manganese and magnesium in the preflamation zone, which not only inhibits the formation of hard deposits, (fouling) of the boiler, an oven, but also combines with the vanadium in the fuel to form a layer relatively smooth on the surfaces of the tubes, reducing the generation of S03, minimizing the availability of Fe and Va to catalyze the formation. This is achieved by dosing additives based on Magnesium and Manganese in relatively low ratios (1 liter of additive per 4,500 liters of fuel oil). But this only reduces the S03 between 25-40%. It is important to note, however, that it does not completely eliminate S03, so that there are still emissions to the chimney; in addition to the potential for condensation corrosion in cold areas. The injection of larger amounts of magnesium and manganese has not led to higher reductions of S03, causing, on the contrary, fouling problems in the boiler and having an excessive cost. This method can be used with many types of combus- tibles and in different types of boilers and process kilns, and can be used in Petrochemical Refineries, Power Plants, etc. Dual treatment has been shown to be more effective in controlling acid conditions than frontal treatments. One reason for this great reactivity is that the additives in the cold zone do not have to pass through the flame before being combined with S03 in the cooler areas of the boiler. In the flame, the frontal additives based on MgO or MgO: Q Al203 do not react with S03 at these temperatures and their effectiveness to react in the posterior zones is diminished having gone through a calcination process. The dry and less hygroscopic ash, product of the dual dosing, reduces corrosion and clogging in the cold zone, and at the same time eliminates acid emissions in the chimney. Moreover, an improvement in the appearance of the visual opacity is obtained, with the consequent elimination of inconveniences and legal complaints, particularly when the plant or is in a tourist, residential or agricultural area, etc. The most practical and least expensive way of executing the method described here is carried out through the injection of an additive containing magnesium and manganese to optimize the combustion, and reduce the amount of S03, so that the amount to be added. MgO is reduced, which neutralizes the condensed S03 and protects against corrosion. In some boilers, a portion of the combustion gases that leaves the superheater zone is recirculated to the combustion zone. In this case the injection of the MgO for the cold zone is carried out after the return of gases. Combining the use of suspension additives containing magnesium and manganese in the combustion zone, with an additive based on MgO in the cold zone, the total suspended particles and S03 are substantially reduced, the emitted particles are dry and non-corrosive, thus preventing damage to the surrounding areas. The visual opacity in the chimney is reduced. The effectiveness of the blower and collectors in the chimney is optimized when MgO is used in the cold zone, and the possibility of a problem of high opacity due to an atmospheric inversion is minimized. With residual fuels a manganese-based additive is used, such additive reduces the amount of carbon in the ashes since manganese acts as a combustion catalyst. This in itself is an advantage since humid carbon readily absorbs S03. In addition, the presence of manganese promotes the operation at low excess air, reducing the conversion of S02 to S03. The additional injection of a powder additive based on MgO in the cold zone is an excellent complement for the total neutralization of S03 and promotes lower gas temperatures, thus increasing efficiency.

PROCESS OF APPLYING DUAL TREATMENT This treatment process involves introducing an additive based on Mg and Mn (in its oxide states) into the preflamation zone, which is injected into the fuel before burners. This additive called frontal has several effects: 1) Reacts with the Vanadium of the fuel and prevents corrosion and fouling by deposits in high temperature; 2) It acts by creating a protective layer in the superheater tubes and isolates the combustion products from the iron surfaces of those tubes, which is a catalyst for the formation of S03; 3) Promotes an operation to lower excess air to be able to burn better the carbon particles generated by combustion. 4) Mg reacts with Vanadium, reducing the amount of Vanadium oxides that are also catalysts of the reaction from S02 to S03. The injection of Magnesium compounds is limited by the fouling potential that this would cause in addition to the increase in inorganic particles emitted into the atmosphere. The mechanism by which Magnesium reduces the amount of S03 involves the formation of Magnesium Sulfonate, which decomposes at temperatures above 815 ° C (1500 ° F) and, because the temperature in the home is above this not only does it cancel the Magnesium's effectiveness in reacting with S03, but it can increase the generation of S03 by decomposing Magnesium Sulfonate. In addition to the preflamable additive, the injection of an additive into the cold zone of the boiler, which contains MgO, is suggested. An amount of MgO and MnO injected into the fuel oil, gives a reduction of 15-25% and this reduction can not be increased more than 80% even with the increase in the dosage. If an amount of MgO is added in the cold zone (example: entry to pre-heaters), and air-steam heaters are closed, the reduction of S03 is 90-100%. This is achieved by using the same amount of MgO required to achieve 40% reductions in S03, but distributing the MgO by 25% in the preflama area and 75% in the cold zone. The active elements of the additives of the dual treatment are Manganese and Magnesium, however these are not handled as such because commercially they are not available. Oxides or hydroxides are usually used because of their ease to be found in the market and at reasonable prices. EXAMPLES The following is a series of practical examples of application of the dual treatment, where the advantages and the scope of the same are observed.

EXAMPLE 1 This test was run for 2 1/2 months, of which 1 month additives were dosed with stable conditions keeping a record of emissions and operation of the unit. The evaluation was carried out by an impartial entity, and fuel oil was consumed typical to that used in Mexico with 3.5% sulfur and 300 ppm vanadium, for a 158 Mw boiler. A liquid additive based on MgO and MnO was applied in the fuel oil at a ratio of 1 lt per 4,500 lts. of fuel oil, and a powder additive based on MgO was injected at the inlet of preheater at a rate of 1 kg per 1000 l of fuel oil.

Results Total Suspended Particles (PST): The results obtained from this parameter showed an average reduction of 37%, observing at the beginning of the dosage a tendency to gradually decrease, remaining more stable after 10 days of starting the dosage. The reduction came to represent up to 45%, it is evident that even with the pose contribution of PST of the same additives the reduction has represented such high values, which gives us an idea of the significant participation in the reduction of PST of the liquid additive.

Visual Opacity: The reduction of the PST had influence in the reduction of the vility of the stack gases that was 50%.

Sulfur trioxide: S03 emissions were eliminated by closing the air-steam heating coils (CAV), which promoted the acid condensation of S03 without causing corrosion problems when neutralized with Coaltrol MZ. In this plant there are problems of emissions of acid particles, which causes corrosion problems in the surrounding areas as well as contributing to the opacity of the flue gases, so that by eliminating the precipitation of acid particles, 2 parameters were reduced.

Free Acidity and pH in ashes: With the application of the Dual Dosing it was pose to practically eliminate the emissions of acid soot even with the closing of the Air-Steam Heaters (CAV). As a logical result, the pH of the ash was increased by almost 2 units (it went from 3.12 without additives to 4.85 with additives).

Thermal efficiency of the boiler: The reduction of the temperature of exhaust gases (THS) by the closure of the CAV's had a significant effect on the efficiency as the heat losses by dry gases decreased significantly. The increase in efficiency was 1.47%, which was reflected in fuel oil consumption. According to the data obtained in the field, the fuel oil saving represented a 3.3% reduction in fuel oil consumption.

Fouling and Corrosion in Air Preheaters: This point was closely followed, not observing any abnormal increase in the differential pressures in preheater that was linked to the Dual Dosage; In addition, during the inspections, the cold part of the preheaters without corrosion was found, even when the CAVs were kept closed.

EXAMPLE 2 A 6-month Dual Dosage evaluation was started at the Manzanillo Thermoelectric Plant, Colima. This test was run using imported fuel oil with percentages of Sulfur less than 2% and 200 ppmv of Vanadium average in a unit of 300 Mw. identify-da as U4. This situation did not alter the behavior of the additive that still obtained positive results using the same relationships discussed in the previous example.

Total Suspended Particles (PST). Significant reductions were still maintained, even though fuel consumption in the United States (San Francisco), Venezuela (Amuaw) and Colombia (Mamonal) of 2% maximum sulfur with national (Salina Cruz) of 3.5% was alternated during these periods. sulfur.

Opacity: Unlike the baseline, the visual opacity remained stable with no gradual increase observed after the cleaning of the unit in October 1994. The average shows a reduction of 60% with respect to the Base Line. The opacity of the U-3 (without additives), even when it is inside in maintenance was always found up to more than 100% with respect to U-4.

Nitrogen oxides: As in the test period, it does not present any reduction. In this test, a chemical luminescence device is used, which is calibrated daily, so its values are reliable.

Sulfur trioxide: S03 emissions in the chimney were reduced by 75%. After correcting problems with the sampling system, the values were practically zero (3ppm).

Free Acidity and pH (1/100): In general, Free acidity continued to be maintained at zero, except for the days when fuel oil with higher Sulfur and vanadium was fed (which caused the values to increase). This increase was immediately controlled by passing a dosing ratio in the cold zone of the boiler. With the dosage the pH values (1/100) were maintained above 1 unit, going from 3.4 in Baseline to 4.2 on average Thermal Efficiency of the Boiler: Keeping the CAV completely closed has promoted that the temperature of the gases in the chimney decrease even more, reaching up to 124 ° C against 171 ° C that was averaged during the Base Line, this reduction of 47 ° C promoted a increase that, according to calculations, is up to 3% with respect to Baseline. This increase results in a decrease in fuel oil consumption. Surveys made to the day tank showed an average reduction of 1.3 tons. daily metrics.

Fouling and Corrosion in the cold zone: During the injection of the additive an increase in the differential pressure and pressure of the home was observed, which forced the generation of the unit to decrease. The unit was stopped for inspection after three months of continuous operation and no plugging of the superheater was found whose origin was totally foreign to the treatment.

EXAMPLE 3 At the "Feo. I. Madero" refinery in Cd. Madero Tamaulipas, a prefix additive based on MgO and MnO was injected and a powder additive based on MgO injected into the combustion gases entering the regenerative air preheater. The treatment was applied to a unit of 120 ton / hr capacity steam, keeping its air-steam heating coils in operation. In 5 years of treatment, this unit maintained an operative availability of between 95 and 100%, the useful life due to corrosion of the preheater was increased by 150%. The emissions of S03 and Free Acidity in ash remain similar to those in Example 1 and 2. The efficiency was not significantly affected when the air-steam coils were not closed.

EXAMPLE 4 At the "Ing. Antonio M. Amor" refinery, the treatment explained in examples 1, 2 and 3 was carried out. At the same time, an injection of a pre-flame additive based on MgO was carried out in another boiler. These tests were carried out in boilers of 200 ton / hr of steam using fuel oil of up to 4% by weight of sulfur and 300 ppm of Vanadium. The results were the following: PARAMETER WITHOUT ADDITIVE DOSAGE ADDITIVE PREFLAMA TO DUAL BASED ON MgO . - SO3 (ppm) Average 24 11 21.3 Max / min 16/8 40/4 .- Free Acidity (mg.H2S04 / g sample) average 31 0.3 2.55 max / min 2/0 15.8 / 0.-PST (mg / m3gases ) average 350 246 NR max / min N.R. .-Opacity (X) average 20 0 N.R. Max / min 5/0 N.R. Combustible Combustible Fuel and Gas In-service coils Outside Op. In Vapor Service Efficiency (Z) 83.4 86 83.8 Comb. 85 71 94 (lt. Comb / ton.Vapor) EXAMPLE 5 At the "Miguel Hidalgo" Refinery in Tula, Hidalgo, the dosage of additives in 4 steam generators of 200 ton / hr of nominal capacity has been maintained. These units generate steam of 1000 ° F and 60 kg / cm2 using fuel oil with 4% sulfur and 300 ppmv of vanadium. Since 1988 an additive based on magnesium and manganese has been injected into the fuel oil at a ratio of 1 lt. of this additive for each 4,500 lts. of fuel oil, sufficient to ensure at least a molar ratio MgO: SO3 of 1: 1 and Mn: V of 0.25: 1. The emissions of S03, total suspended particles and Ash Free Acidity of the 4 steam generators are similar to those in Example 1 and 2, highlighting recently the CB3 which operated 16 continuous months without problems of corrosion and / or fouling of the superheater zone and regenerative air preheater. Here a number of examples have been presented with which the benefits of this invention are demonstrated. It is possible that, from these, many variations can be made, but each of them can not depart from the essence of this invention protected by the tenor of the following claims:

Claims (10)

RE I V I ND I C AC I O N S

1. - Dual dosage process of additives for the reduction of polluting emissions, combustion control and increase of thermal efficiency in steam generators or furnaces that use residual fuels, which comprises the following stages: A) combustion of the fuel in the presence of a first amount of additive containing magnesium, manganese, compounds based on these elements or the combination thereof; B) the transportation of these combustion gases through the convective zone (superheaters, reheaters, convection pipes, etc), to a zone of lower temperature (regenerative air pre-heater, economizer, etc); and optionally C) the simultaneous injection into the combustion gases of an additional amount of additive based on magnesium, magnesium compounds or the combination thereof.

2. The method according to claim 1, wherein said fuel is burned in a furnace or furnace and its gases are transported through the zone of superheater (high temperature) to the zone of economizers and preheaters of air (low temperature), and expelled from it through the chimney.

3. The process according to claim 1, wherein the additive described in step C) is applied in the zone of low temperature, which is at a temperature within the range of 90 to 550 ° C.

4. The method according to claim 1, wherein the additive of step C) is at least in a molar ratio of MgO to S03 of between 1: 1 and 4: 1.

5. The process according to claim 1, wherein the application of these additives cover the operational variations that could generate higher S03 and that comply with an effective neutralization of the condensed acid.

6. The process according to claim 1, wherein the additive of step A) comprises only magnesium-containing substances, magnesium-derived compounds or a combination thereof.

7. The process according to claim 1, wherein the additive of step A) comprises only substances containing manganese, manganese compounds, or a combination thereof.

8. The process according to claim 6, wherein the additive of step (A) is in a molar ratio of Mg: V of between 0.25: 1 and 1: 1 9.- The compliance procedure with claim 7, wherein the additive of step A is in a molar ratio of Mn: V of between 0.25: 1 and 1: 1. 10. The process according to claim 1, wherein a portion of the combustion gases are recirculated to the combustion zone, and in which a component of a substance that may consist of magnesium, magnesium compounds , or a combination of these apply to the posterior zone of this gas recirculation.