FIELD OF THE INVENTION:

The present invention relates to descaling and antifouling formulations effective for removing both metal and hydrocarbon contents of scales with minimum amount of residual mass. Further, the present invention also relates to process for preparing the descaling and antifouling formulations.

BACKGROUND OF THE INVENTION:

Deposition of lower thermal conductivity material such as particulate matter, coke, metal impurities and fouling material on heater tubes is a common phenomenon in the high temperature boilers and furnaces. During the combustion process and depending on the type of fuel oil and operating temperature conditions the vanadium, alkali-metal sulphates and aluminium silicates form hard deposits.

Further, the flue gases contain finely divided carbon, sulphur dioxide, sulphur trioxide and nitrogen oxides. The incomplete combustion in fired heaters and boilers, leads to the formation of deposits on heat transfer surfaces. The unburnt carbon and sulphur form a softer and sometimes more sticky deposits to which other unburned particles are deposited over the sticky deposits, thereby increasing the thickness of the deposits and leads to heat transfer reduction.

Thus, these deposits contain unburned carbon, alkali-metal sulphates, aluminium silicates or sulphuric acid and vanadium. These deposits are generally called scales and as the thickness of the scales increases, the heat exchange between flue gases and metal surface of the heater tubes reduces and which ultimately reduces the temperature of the crude oil flowing inside the heater tube. To maintain the desired crude oil temperature and optimum skin temperature, it is necessary to provide additional amount of energy that result in consumption of more amount of fuel oil. Thus, to avoid additional amount of energy required for maintaining the optimum skin temperature, effective and periodic removal of scales is essential. Hence, the deposits in the form of scale are highly objectionable, since they are poor conductors of heat, causes reduced efficiency, and are often responsible for burned tubes or plates. The main problems caused by furnace scales are increase in tube wall temperature, hence, furnace heater tube ruptures. Further, the scales decrease the overall furnace thermal efficiency, hence, increase in energy cost and loss of reliability.

WO2017085748A1 discloses anti-fouling composition including a metallic component comprising of at least one alkali metal salt and a non-metallic component and method for preparation of anti-fouling composition. Wherein, the metallic component weight ratio in the composition is in the range of 50 to 95% and the non-metallic ratio in the composition is in the range of 5 to 50%. In one example, metallic component is a combination of sodium nitrate and potassium nitrate with a weight ratio in the range of 1 : 1 to 4: 1 and a non-metallic component selected from the group of urea, oxalic acid, succinic acid, tartaric acid, EDTA, ammonium oxalate, ammonium nitrate, ammonium acetate, ammonium sulfate, and sugar.

CN1326985C discloses multi-purpose cleaning mixture consisting of phosphoric acid, oxalic acid, citric acid, urea, and water. It can remove scale deposit, oil deposit and dirt attached on metal, sanitary ceramics, and kitchen utensils.

It is also noted that the sulphur in the fuel is oxidized to sulphur trioxide, which reacts with water vapors to form sulphuric acid condensable at the metallic surface when its temperature is below the dew point. Generally, this situation arises when flue gas temperature is above its dew point and combustion dust isolates heat exchange surface. The sulphuric acid causes corrosion and the air heaters, the technical pipelines and the stacks are particularly vulnerable to this type of low temperature corrosion. Further, vanadium oxide with a very low melting point forms super-hard deposits primarily in the areas of particularly high heat. Such deposits are very difficult to remove, and they are a source of high temperature corrosion. Vanadium oxide is also a catalyst of the reaction for the conversion of sulphur dioxide to trioxide.

The problem of scale formation increases when the fired heater operates at high load for a long time. The scale formation often causes unexpected shutdowns for future maintenance and reduces the residual operation life of the pipes due to the high and low temperature corrosion. In any furnace, boilers or fired heaters there are three sections depending upon the type of scale deposition such as a radiation section, a middle section, and a convection section. For example, in case of radiation section, (nearest to the burner) the deposited scale has maximum content of metal and that of convection section (upper most section) has carbon rich scales deposition. In the middle section the scale has almost equal amount of hydrocarbon and metal. Accordingly, different sections have different scales and thus each section requires different descaling treatment. At the same time, it is also important to protect the furnaces and boiler parts from low temperature corrosion and high temperature corrosion.

Hence, it is important to develop environment friendly descaling formulations with reduced maintenance cost. It is also important to develop cost effective descaling formulations with improved performance, and which can effectively remove deep and tuff layers of scales and with enhanced sustainability. Further, it is also important to develop novel descaling formulations which can be easily applied to remove deep and tuff layers of scales from furnaces and boilers.

TECHNICAL ADVANTAGES OF THE INVENTION:

One advantage of the present invention is to provide descaling and antifouling formulations effective for removing both metal and hydrocarbon contents from a radiation section of furnace, a middle section of furnace, a convection section of furnace, and a boiler.

Another advantage of the present invention is to provide descaling and antifouling formulations which are basic in nature and thus protects the metal parts from corrosion. Yet another advantage of present invention is to provide descaling and antifouling formulations which have descaling efficiency above 65%.

Another advantage of present invention is to provide descaling and antifouling formulations which can be used in liquid form and can be applied through automatic sprayer system.

SUMMARY OF THE PRESENT INVENTION:

The present disclosure provides a descaling and antifouling formulation including an ammonium oxalate in a range of 5 to 65 weight percent, a nitrogen compound in a range of 15 to 90 weight percent, wherein the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), or urea, and optionally a nitrate salt in a range of 5 to 20 weight percent.

Wherein, ethylenediaminetetraacetic acid (EDTA) is an ethylenediaminetetraacetic acid ammonium salt. Wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate, Magnesium Nitrate, or a combination thereof.

Further, the said formulation includes the ammonium oxalate in 5 weight percent, the Ammonium EDTA is 90 weight percent, and the nitrate salt is 5 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate and a mixture thereof.

In an embodiment, the formulation includes ammonium oxalate in 65 weight percent, urea in 15 weight percent, and nitrate salt in 20 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate and a mixture thereof.

Further, in another embodiment, the formulation includes ammonium oxalate in 20 weight percent, and urea in 80 weight percent.

Further, the said formulation is soluble in water and descales metals and hydrocarbons from a radiation section of furnace, a middle section of furnace, a convection section of furnace, and a boiler. The formulation is basic is nature and thus protects the metallic part of radiation section, a convection section, and a boiler from corrosion. The said formulation provides descaling efficiency above 65%.

Further, present disclosure provides a process for preparing a descaling and antifouling formulation, wherein, the said process includes steps of prepare a salt mixture by mixing ammonium oxalate, a nitrate salt, and optionally a nitrogen compound selected from ethylenediaminetetraacetic acid (EDTA), or urea in a crucible and grind thoroughly with the help of mortar pestle. Wherein, the said salt mixture includes ammonium oxalate in a range of 5 to 65 weight percent, a nitrogen compound in a range of 15 to 90 weight percent, wherein the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), or urea, and a nitrate salt in a range of 5 to 20 weight percent. Wherein, the ethylenediaminetetraacetic acid (EDTA) is an ethylenediaminetetraacetic acid ammonium salt.

Wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate, Magnesium Nitrate, or a combination thereof.

Further, the said salt mixture includes the ammonium oxalate in 5 weight percent, the Ammonium EDTA is 90 weight percent, and the nitrate salt is 5 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate and a mixture thereof.

In an embodiment, the said salt mixture includes ammonium oxalate in 65 weight percent, urea in 15 weight percent, and nitrate salt in 20 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate and a mixture thereof.

Further, in another preferred embodiment, the said salt mixture includes ammonium oxalate in 20 weight percent, and urea in 80 weight percent.

Then transferring the salt mixture into the 50 ml round bottom flask and connect the round bottom flask with a rotary evaporator. Removing the moisture from the salt mixture under reduced pressure while maintaining a water bath temperature at 60 °C. Taking out the salt mixture from the round bottom flask with the help of spatula and storing the same in a sample vial.

OBJECTIVES OF THE PRESENT INVENTION:

The primary objective is to develop descaling and antifouling formulations having enhanced descaling efficiency and can remove deposited scales, with longer sustainability of product.

Another objective is to develop descaling and antifouling formulations effective for removing metal rich scales, deposits in radiation section of the furnace.

Another objective is to develop descaling and antifouling formulations effective for removing carbon rich scales, deposits in convection section of the furnace. Another objective is to develop descaling and antifouling formulations effective for removing scales and deposits from boilers.

Another objective is to develop descaling and antifouling formulations effective for removing both metal and hydrocarbon contents of scale with minimum amount of residual mass.

Another objective is to develop descaling and antifouling formulations which can be used in liquid form such as auto chemical spraying system for on-line cleaning of boilers.

BRIEF DESCRIPTION OF THE DRAWING:

To further clarify advantages and aspects of the present descaling formulations, a more particular description of the present descaling formulations will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawing(s). It is appreciated that the drawing(s) of the present integrated process depicts only typical embodiments of the invention and are therefore not to be considered limiting of its scope.

Figure 1: illustrates a diagrammatic representation of different sections in a furnace; and

Figure 2: illustrates an XRD plot for different scale samples;

Figure 3: illustrates a TGA plot comparing different descaling formulations;

Figure 4: illustrates a TGA plot for radiation section descaling formulations (Scale M, EDTA, A5-M1-0A, UA0-R2, UA0-R1); and

Figure 5: illustrates a TGA plot for convection section descaling formulations (A5-M1-0A, IFS- ED).

DESCRIPTION OF THE INVENTION:

Furnaces have different sections and deposits on each section have different chemical nature and properties. These furnace sections are described below with the deposits and their chemical nature. Further, figure 1 depicts diagrammatic representation of different sections inside a furnace.

Radiation section

The radiant section is where the tubes receive almost all its heat by radiation from the flame. In a vertical, cylindrical furnace, the tubes are vertical. Tubes can be vertical or horizontal, placed along the refractory wall, in the middle, or arranged in cells. Studs are used to hold the insulation together and on the wall of the furnace. It has been found that the scales deposited in this region have maximum content of metal because this section is nearest to the flame inside the furnace.

Convection section

The convection section is located above the radiant section where it is cooler to recover additional heat. Heat transfer takes place by convection here, and the tubes are finned to increase heat transfer. The area of the radiant section just before flue gas enters the shield section and into the convection section called the bridge zone.

Fuel flows into the burner and is burnt with air provided from an air blower. There can be more than one burner in a particular furnace which can be arranged in cells which heat a particular set of tubes. Burners can also be floor mounted, wall mounted, or roof mounted depending on design. The flames heat up the tubes, which in turn heat the fluid inside in the first part of the furnace known as the radiant section or firebox. In this chamber where combustion takes place, the heat is transferred mainly by radiation to tubes around the fire in the chamber.

Accordingly, the present disclosure provides descaling and antifouling formulations for descaling metals as well as hydrocarbons from a radiation section of furnace, a middle section of furnace, a convection section of furnace, and a boiler.

According to the main embodiment, the present disclosure provides descaling and antifouling formulations including an ammonium oxalate in a range of 5 to 65 weight percent, nitrate salt in a range of 5 to 20 weight percent, and a nitrogen compound in a range of 15 to 90 weight percent, wherein the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), or urea.

Wherein, the ethylenediaminetetraacetic acid (EDTA) is an ethylenediaminetetraacetic acid ammonium salt. Wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate, Magnesium Nitrate, or a combination thereof. Further, the said formulation includes the ammonium oxalate in 5 weight percent, the Ammonium EDTA is 90 weight percent, and the nitrate salt is 5 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate and a mixture thereof.

In an embodiment, the formulation includes ammonium oxalate in 65 weight percent, urea in 15 weight percent, and nitrate salt in 20 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate and a mixture thereof.

Further, in another embodiment, the formulation includes ammonium oxalate in 20 weight percent, and urea in 80 weight percent.

Further, the said formulation is soluble in water and descales metals and hydrocarbons from a radiation section of furnace, a middle section of furnace, a convection section of furnace, and a boiler. The formulation is basic is nature and thus protects the metallic part of radiation section, a convection section, and a boiler from corrosion and the formulation provides descaling efficiency above 65%.

Experiment and Methodology

The study as disclosed herein below is carried out to find out the suitable descaling formulations which can be used for different furnace sections and to descale metals and hydrocarbon deposits.

Refinery scales collection & characterization

Scale samples were collected from refinery crude distillation unit furnaces during a major shutdown of a crude oil distillation unit in the four-year period of operation. The collection was performed following water circulation and steam purging, mechanical cleaning of the tube during shutdown period. Three different scale samples are collected from various sections of furnace in the refinery. Scale samples were grinded properly using the mortar pestle and their chemical characterization is carried out.

Metal analysis of scale samples

Scale samples are collected possessing different thickness and color ranging from black to brown in color. Metal analyses are carried out by using ICP-OES instrument. All scales are containing above 80% metallic and non-metallic scales only and remaining are carbon scales. Elemental analysis of three different scale materials is shown in below table 1.

Table 1: Elemental and metal analysis of scale samples

“Scale C” (FURNO-VR) scales are slightly black in color due to high carbon content and “Scale- M” (FURNO-CDU-2) scales are dark brown color scales because of high percentage of metallic and sulphur compounds. Whereas “Scale S” (FURNO-S-B) scales are light brown in color due to more than 50% content of Silicon compounds.

XRD analysis of scale materials

X-ray diffraction analytical technique has been used for identification of various compounds which are present in scale samples and identification of their crystalline nature. XRD profiles of various scale removal formulations are shown in Figure 2.

XRD plot shows that all the scale samples are crystalline in nature. XRD peaks of Scale S scale samples are identified as molten sulphur, silicon, silicon carbide and Iron oxide (FeO). XRD peaks of Scale-M scale samples are identified as nickel sulfide (NiS), molten sulphur, silicon, and iron sulphide (FeS). XRD peaks of Scale C identified as silicon carbide and hematite (Fe3O4). From the ICP metal analysis data it can also be confirmed that the above-mentioned compounds are present in respective scale materials.

Synthesis steps for dry descaling salt formulation

Weigh the individual salt and mix all the components in crucible and grind thoroughly with the help of mortar pestle, transfer the salt mixture into the 50ml round bottom flask and connect the round bottom flask having salt mixture to a rotary evaporator, remove the moisture under reduced pressure while maintaining the water bath temperature at 60 °C, take out the salt mixture from the round bottom flask with the help of spatula and store it in a sample vial.

Further, it is also important to ensure removal of water completely from salts as moisture is going to change the proportion of weight percentage, which is a very crucial part. At the same time the mixture should be homogeneous, so the other way to do this is crush and mix salt(s) mixture properly in mortar pestle and then keep in 120° C oven for some time (30-45 minutes), again crush it after it cools down and keep the same way in oven. Follow the same process for about 4 to 5 times and immediately keep in closed vials and cover the lid with paraffin so as to ensure zero moisture absorbance.

In detail, present disclosure provides a process for preparing a dry descaling and antifouling formulation, wherein, the said process includes steps of preparing a salt mixture by mixing ammonium oxalate, a nitrogen compound selected from ethylenediaminetetraacetic acid (EDTA), or urea, and optionally a nitrate salt in a crucible and grinding thoroughly with the help of mortar pestle. Wherein, the said salt mixture includes ammonium oxalate in a range of 5 to 65 weight percent, a nitrogen compound in a range of 15 to 90 weight percent, wherein the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), or urea, and optionally a nitrate salt in a range of 5 to 20 weight percent.

Wherein, the ethylenediaminetetraacetic acid (EDTA) is an ethylenediaminetetraacetic acid ammonium salt. Wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate, Magnesium Nitrate, or a combination thereof.

Further, the said formulation includes the ammonium oxalate in 5 weight percent, the Ammonium EDTA is 90 weight percent, and the nitrate salt is 5 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate and a mixture thereof.

In an embodiment, the formulation includes ammonium oxalate in 65 weight percent, urea in 15 weight percent, and nitrate salt in 20 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate and a mixture thereof. Further, in another embodiment, the formulation includes ammonium oxalate in 20 weight percent, and urea in 80 weight percent.

Then transferring the salt mixture into the 50 ml round bottom flask and connect the round bottom flask with a rotary evaporator. Removing the moisture from the salt mixture under reduced pressure while maintaining a water bath temperature at 60 °C. Taking out the salt mixture from the round bottom flask with the help of spatula and storing the same in a sample vial.

Preparation of 6 wt.% of aqueous descaling salt solution

Take 1 gm of dry descaling salt formulation and then take 50 ml of glass beaker and pour the descaling formulation in the beaker. Measure 15.5 ml of distilled water using measuring cylinder and pour the distilled water slowly in the glass beaker. Keep the beaker in ultra sonicator for 1 minute time. Once the solute is completely mixed in solvent, transfer the descaling solution into the sample vial for storage.

Offline descaling study for different dry descaling salt

Different descaling salts (as indicated in Table 2) and scale material are taken in 1 : 1 weight ratio. Specifically, dry descaling salt and Scale M material are weighed separately by using weighing balance and both the scale material and descaling salt are mixed thoroughly by using mortar pestle. Taking the empty weight of the alumina crucible. Transferring the descaling salt and scale mixture into the alumina crucible and taking the weight of crucible with sample. Placing the alumina crucible in the muffle furnace and start heating. The temperature program given to the furnace has conditions such as set point temperature = 800 °C, ramp rate = 10 °C /min, and holding time is equal to 2 hour.

Once the furnace reaches the room temperature, the alumina crucible is taken out from the furnace and the weight of crucible is measured. Calculating the offline descaling efficiency of each formulation based on the initial and residual weight of the scale and descaling salt mixture.

The formula used for calculating thermal offline descaling efficiency is:

Thermal descaling Efficiency

(Amount of scales taken - Residual amount of scales)

= - - - * 100

Amount of scales taken Offline descaling efficiency is combination of both thermal descaling efficiencies due to high temperature heating and chemical descaling efficiency due to presence of chemical formulation which enhances the rate of evaporation scales by either forming low thermal stable compounds with metallic compounds or either increasing rate of oxidation of scale constituents or reduction of melting point metal components.

To find out suitable descaling and antifouling formulations, several descaling formulations were synthesized, and their offline descaling efficiency was studied using descaling protocol as disclosed hereinabove. Those formulations that has shown better descaling efficiency (more than 60%), for those inductively coupled plasma - optical emission spectrometry (ICP-OES), C, H, N, S, O data is collected and analyzed to find out the percent removal of metals and hydrocarbon by those selected descaling formulation. Apart from that and to find out the decomposition temperature and residual mass of the formulation, TGA at 800 °C under N2 atmosphere is carried out. Through these TGA studies it can be confirmed that the descaling salt will not leave any residue behind in the furnace while operation and will decompose up to this temperature limit. In addition to these tests, TGA studies of salt and scale mixture (1: 1) were studied to confirm the residual mass after treatment left at 800 °C under nitrogen atmosphere and 10 °C ramp rate. For the formulations that shown better descaling efficiency (more than 60%) solubility in water at room temperature is found out. Apart from solubility, pH in water at 5% concentration is measured to confirm that the working pH of the formulation should not be acidic. The reason for not preferring acidic solution of formulation is that in acidic medium the phenomenon corrosion is catalyzed. Accordingly, to avoid such consequences the use of acidic solution should be avoided.

The protocol followed for offline descaling studies is like what is used for powder descaling efficiency. Mixture (1:1) scale and descaling formulation kept at 800 °C in a furnace under 02 atmosphere keeping 10 °C ramp per minute and kept for 2 hour.

Below table-2 provides list of different descaling formulations which are synthesized, and their offline descaling efficiency is determined to find out the suitable descaling and antifouling formulation. Table 2: Offline descaling efficiency of different dry descaling salt formulations

From the above table-2 representing different offline descaling formulations it can be concluded that the formulations are showing better descaling efficiency i.e., more than 65% among all other descaling formulations. The ICP-OES data and CHNSO, TGA data is measured for these formulations.

Solubility Studies for different dry descaling salt formulations:

Further, the solubility study is carried out for different dry descaling salt formulations as indicated in below table 3. Wherein, solubility is measured for different dry descaling salt formulations dissolved in distilled water at room temperature taking 5% concentration in distilled water and pH of same solution is measured. Before measuring any property homogenous mixing of the descaling salt is ensured. The compositions that are soluble in water and are having either neutral or slightly basic pH are selected for descaling and antifouling purpose because the highly acidic solution can lead to corrosion.

Table 3: Solubility and pH of different dry descaling salt formulations

Table-2 indicates that the formulations are showing better descaling efficiency i.e., more than 65% among all other descaling formulations and now Table-3 indicates formulations that show acceptable pH. - Elemental analysis of scales before and after treatment with the selected descaling formulations The descaling formulations which have shown better descaling abilities and have acceptable pH for them metal and hydrocarbon removal analysis before and after treatment was done. In this analysis it can be noticed that the Ammonium EDTA is effective in removing both metals and hydrocarbons effectively. Further, Ammonium EDTA is soluble in water and EDTA is not soluble in water. Tabular representation for the same is provided in below Table-4.

Table 4: Elemental Analysis of Scales Before and After Treatment

From the above study and results of table 2-4, three descaling formulations have been selected and prepared which are tabulated in below table 5. The thermal stability is calculated for these three descaling formulations using TGA by the formulation and scale in 1 : 1 and carry out the analysis at 10 °C ramp rate under nitrogen atmosphere till 900 °C. The residual mass left is found to be negligible till 900 °C. The graph as mentioned in figure 3 indicates the activity of mass change with respect to temperature change for these three descaling formulations as selected and prepared by combining suitable descaling components as identified from the study carried out on different descaling components and compositions.

Table 5: Variation of residual mass with temperature for three selected descaling formulations

All the salts started decomposing from 100 °C temperature but the rate of decomposition of Formulation 2 is high at lower temperatures (below 600 °C), whereas, Formulation 1 is having high rate of decomposition in the range 600-800 °C. In the temperature range from 25-800 °C, at each temperature Formulation 3 is having more weight loss than Formulation 2 and Formulation 1. The residual mass at 800 °C is almost 3 wt.% is lower for Formulation 2 than Formulation 1.

If a comparison of residual mass is done then in case of Formulation 3 the residual mass is almost negligible at 800 °C, ensuring that during treatment it is not going to leave any residue formation inside the furnace.

Comparison of percentage metal and hydrocarbon removal of scales

The metal and CHNSO data for these three descaling formulations is compared and from the data it can find out how much removal of the metal and hydrocarbon entities is taking place very conveniently and effectively. On moving from formulation 1 to the formulation 3, the percentage removal is getting better. Table 6 down below compares the data for the same.

Table 6: Comparison of offline descaling efficiency of various descaling formulations

Radiation Section Descaling Salt

Radiation Section is the lowest section in a furnace where the scales are found to be rich in metal content. This section is nearest to the burner and hence most of the hydrocarbon are decomposed off there already, so the maximum amount present is metals like Al, Fe, Ni, Si and V. These metals are expected to be in the form of oxides. The scale formulation coded as Scale M has a greater number of metals in it relative to hydrocarbon content. The complete elemental analysis of the scale formulation coded as Scale M is provided in below table 7.

Table 1: Elemental Analysis of Scale M scales

Offline Descaling Efficiency

The offline descaling efficiency of different descaling salts for radiation section was measured using descaling protocol as hereinbefore mentioned and data is mentioned in below Table 8. Table 2: Offline descaling efficiency of different descaling salts for radiation section The data shows that apart from sodium hydroxide all the formulations provide better than 65% efficiency. For the formulations that has shown promising descaling efficiency, for those metal and hydrocarbon removal efficiency is also measured.

Table 3: Elemental Analysis of Metal and Hydrocarbon Removal

TGA Analysis for Residual Mass Evaluation

TGA studies are carried out to find out the residual mass of the formulations in working conditions. It can be noticed that the residual mass is zero for formulation UAO-R2 and UA0-R1 at 800°C temperature. Moreover, the UAO-R2 has descaling efficiency around 68.68 and UA0-R1 has descaling efficiency around 67.96.

Table 4: TGA Analysis for radiation formulations The graph as mentioned in figure 4 indicates the activity of mass change with respect to temperature change for the above identified descaling salts. Table 5: pH and Solubility Analysis

From the above data it is analyzed that the pH of the finalized formulation is not too acidic rather it is more towards neutral pH hence it can be used as an effective formulation for radiation section.

Convection Section Descaling Salt

Convection section is upper section in the furnace that has maximum amount of carbon among rest of the metal contents. Accordingly, in the convection section scales deposits contain maximum content of carbon. As discussed in table 1 it can be understood that scale coded as Scale C has rich carbon content (14.2%) and hence for this purpose separate formulations are required. The content of Scale C formulation is again mentioned in below table 12.

Table 6: Elemental composition of Scale C formulation

Offline descaling efficiency The same descaling protocol is used to identify the descaling salt for the convection section what was used for other formulations and among those, the best ones are further tested for TGA, ICP- OES, C, H, N, S, O.

Table 13: Offline descaling efficiency

The formulations as tested above in table 13 show almost more than 65% overall offline efficiency. The testing was done with Scale C that has maximum content of carbon up to 14%. To find out the percent removal of CHNS and oxygen content from the scale C, CHSO data is collected and the data is analyzed. Table 7: TGA Analysis

The residual mass for the formulations is approximately negligible i.e., less than 10 %. It can be concluded that the residual mass during operation due to these descaling formulations is negligible. The graph as mentioned in figure 5 indicates the activity of mass change with respect to temperature change i.e., TGA plot for convection section descaling formulations.

Based on the above study and experimentation, the final descaling and antifouling formulations have been identified which provide descaling efficiency above 65%. Further, the final descaling formulations as identified provides efficient descaling of metals as well as carbon deposits on different parts of the furnace and the boiler.

Table 15: Finalized Different descaling Formulations, their Composition and Efficiency

Abbreviations: