Claims:1. A dry descaling and antifouling formulation comprising:
ammonium oxalate in a range of 5 to 30 weight percent,
a nitrogen compound in a range of 15 to 90 weight percent, wherein the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), urea, or a combination thereof;
a nitrate salt in a range of 10 to 70 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate, Magnesium Nitrate, or a combination thereof.

2. The formulation as claimed in claim 1, wherein, the ammonium oxalate is 5 weight percent, nitrogen compound is 90 weight percent; and the nitrate salt is 5 weight percent.

3. The formulation as claimed in claim 2, wherein, the nitrogen compound is ethylenediaminetetraacetic acid (EDTA)

4. The formulation as claimed in claim 2, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate, or a combination thereof.

5. The formulation as claimed in claim 4, wherein, the combination is a solar salt having 60 weight percent Sodium Nitrate, and 40 weight percent Potassium Nitrate.

6. The formulation as claimed in claim 1, wherein, the ammonium oxalate is 30 weight percent, nitrogen compound is 30 weight percent, and the nitrate salt is 40 weight percent.

7. The formulation as claimed in claim 6, wherein, the nitrogen compound is urea.

8. The formulation as claimed in claim 6, wherein, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate, or a combination thereof.

9. The formulation as claimed in claim 6 to claim 8, wherein, the ammonium oxalate is 30 weight percent, nitrogen compound is 30 weight percent, Sodium Nitrate is 30 weight percent, and Magnesium Nitrate is 10 weight percent.

10. The formulation as claimed in claim 6 to claim 9, wherein, the formulation further comprises oxalic acid.

11. A process for preparing a dry descaling and antifouling formulation, wherein, the said process comprises steps of:
preparing a salt mixture by mixing ammonium oxalate, a nitrate salt, and a nitrogen compound selected from ethylenediaminetetraacetic acid (EDTA), or urea in crucible and grind thoroughly with the help mortar pestle;
transferring the salt mixture into a 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; and
taking out the salt mixture from the round bottom flask with the help of spatula and storing it in a sample vial.

12. The process as claimed in claim 11, wherein, the said salt mixture comprises:
ammonium oxalate in a range of 5 to 30 weight percent,
a nitrogen compound in a range of 15 to 90 weight percent, wherein the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), urea, or a combination thereof; and
a nitrate salt in a range of 10 to 70 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate, Magnesium Nitrate, or a combination thereof.

13. The process as claimed in claim 12, wherein, the ammonium oxalate is 5 weight percent, nitrogen compound is 90 weight percent; and the nitrate salt is 5 weight percent.

14. The process as claimed in claim 13, wherein, the nitrogen compound is ethylenediaminetetraacetic acid (EDTA)

15. The process as claimed in claim 13, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate, or a combination thereof.

16. The process as claimed in claim 15, wherein, the combination is a solar salt having 60 weight percent Sodium Nitrate, and 40 weight percent Potassium Nitrate.

17. The process as claimed in claim 12, wherein, the ammonium oxalate is 30 weight percent, nitrogen compound is 30 weight percent, and the nitrate salt is 40 weight percent.

18. The process as claimed in claim 17, wherein, the nitrogen compound is urea.

19. The process as claimed in claim 17, wherein, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate, or a combination thereof.

20. The process as claimed in claim 17 to claim 19, wherein, the ammonium oxalate is 30 weight percent, nitrogen compound is 30 weight percent, Sodium Nitrate is 30 weight percent, and Magnesium Nitrate is 10 weight percent.

21. The process as claimed in claim 17 to claim 20, wherein, the formulation further comprises oxalic acid.
, Description: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. Specifically, the present invention relates to descaling and antifouling formulations which can be utilized in dry powder form. Further, the present invention also relates to process for preparing the dry 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 and design a prototype for the evaluation of surface coating chemicals. Further, it is also important to develop novel descaling formulations and to evaluate their efficiency as an effective anti-fouling coating.

Further, it is also important to develop novel and cost-effective dry powder chemical formulations with effective removal of deep layer scales and with enhanced sustainability. Further, it is also important to apply the descaling and antifouling formulations in dry form so that the continuous removal of scales can be achieved without stopping the operations.

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 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 powder form. Another advantage of present invention is to develop environment friendly descaling and antifouling formulations with reduced maintenance cost.
Another advantage of present invention is to develop novel and cost-effective dry powder chemical formulation with effective removal of deep layer scales and with enhanced sustainability.

SUMMARY OF THE PRESENT INVENTION:
The present disclosure provides a descaling and antifouling formulation including an ammonium oxalate in a range of 5 to 30 weight percent, a nitrogen compound in a range of 15 to 90 weight percent, and a nitrate salt in a range of 10 to 70 weight percent.

Wherein, the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), urea, or a combination thereof. 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 nitrogen compound 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. Wherein, the combination is a solar salt having 60 weight percent Sodium Nitrate, and 40 weight percent Potassium Nitrate.

In an embodiment, the formulation includes ammonium oxalate in 30 weight percent, nitrogen compound in 30 weight percent, and nitrate salt in 40 weight percent. Wherein, the nitrogen compound is urea and, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate and a combination thereof.

Further, in a preferred embodiment, the formulation includes ammonium oxalate in 30 weight percent, nitrogen compound is 30 weight percent, Sodium Nitrate is 30 weight percent, and Magnesium Nitrate is 10 weight percent.

Further, in another embodiment, the formulation includes oxalic acid.

Further, the said formulation is insoluble in water and descales metals and hydrocarbons from a furnace, and a boiler. 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 preparing a salt mixture by mixing ammonium oxalate, a nitrate salt, and 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 30 weight percent, a nitrogen compound in a range of 15 to 90 weight percent, and a nitrate salt in a range of 10 to 70 weight percent. Wherein, the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), urea, or a combination thereof. 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 nitrogen compound in 90 weight percent, and the nitrate salt in 5 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate and a mixture thereof. Wherein, the combination is a solar salt having 60 weight percent Sodium Nitrate, and 40 weight percent Potassium Nitrate.

In an embodiment, the said salt mixture includes ammonium oxalate in 30 weight percent, nitrogen compound is 30 weight percent, and nitrate salt in 40 weight percent. Wherein, the nitrogen compound is urea and, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate and a combination thereof.

Further, in a preferred embodiment, the said salt mixture includes ammonium oxalate in 30 weight percent, nitrogen compound is 30 weight percent, Sodium Nitrate is 30 weight percent, and Magnesium Nitrate is 10 weight percent.

Further, in another embodiment, the said salt mixture includes oxalic acid.

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, as well as carbon rich scales.

Another objective is to develop novel and cost-effective dry powder chemical formulation with effective removal of deep layer scales and with enhanced sustainability.

Another objective is to develop descaling and antifouling formulations effective for removing scales and deposits from boilers as well as from furnaces.

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 dry powder form for effective removal of scales using compressed air medium

BRIEF DESCRIPTION OF THE DRAWING:

To further clarify advantages and aspects of the invention,

Figure 1: illustrates an XRD plot for different scale samples;
Figure 2: illustrates a TGA plot comparing different Descaling formulations;
Figure 3: illustrates a diagrammatic representation of different sections in a furnace;
Figure 4: illustrates a TGA plot for powder descaling formulations (A5-M1-OA, AM-EDTA, EDTA-SS-OA) and scale (Scale M); and
Figure 5: illustrates a TGA plot for 100% powder descaling formulations (A5-M1-OA, EDTA-SS-OA, AM-EA).

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 3 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 boiler as well as from different section of a furnace.

According to the main embodiment, the present disclosure provides descaling and antifouling formulations including an ammonium oxalate in a range of 5 to 30 weight percent, a nitrogen compound in a range of 15 to 90 weight percent, and a nitrate salt in a range of 10 to 70 weight percent.

Wherein, the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), urea, or a combination thereof. 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 nitrogen compound 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. Wherein, the combination is a solar salt having 60 weight percent Sodium Nitrate, and 40 weight percent Potassium Nitrate.

In an embodiment, the formulation includes ammonium oxalate in 30 weight percent, nitrogen compound is30 weight percent, and nitrate salt in 40 weight percent. Wherein, the nitrogen compound is urea and, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate and a combination thereof.

Further, in a preferred embodiment, the formulation includes ammonium oxalate in 30 weight percent, nitrogen compound is 30 weight percent, Sodium Nitrate is 30 weight percent, and Magnesium Nitrate is 10 weight percent.

Further, in another embodiment, the formulation includes oxalic acid.

Further, the said formulation can be used in dry powder form 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 said 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 scales materials is shown in below table 1.

Table 1: Elemental and metal analysis of scale samples
S. No. Scale Code C (%) H (%) N (%) S (%) O (%) Al (%) Si (%) Ni (%) Fe (%) V (%) Total (%) Type
1 Scale S 1 1.1 ND 3 15.4 2.1 55.1 0.6 1.8 0.1 78.1 Silicon Rich
2 Scale M ND 1.7 ND 12.7 42.4 3.8 17.1 9.7 4 2.7 94.1 Metal Rich
3 Scale C 14.2 0.9 ND ND 31.6 2.4 5.3 ND 3.3 ND 57.7 Carbon Rich

“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 1.

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 necessary 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 salts 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 some 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, and 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 30 weight percent, a nitrogen compound in a range of 15 to 90 weight percent, and a nitrate salt in a range of 10 to 70 weight percent. Wherein, the nitrogen compound is selected from ethylenediaminetetraacetic acid (EDTA), urea, or a combination thereof. 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 nitrogen compound in 90 weight percent, and the nitrate salt in 5 weight percent, wherein, the nitrate salt is selected from Sodium Nitrate, Potassium Nitrate and a mixture thereof. Wherein, the combination is a solar salt having 60 weight percent Sodium Nitrate, and 40 weight percent Potassium Nitrate.

In an embodiment, the said salt mixture includes ammonium oxalate in 30 weight percent, nitrogen compound is30 weight percent, and nitrate salt in 40 weight percent. Wherein, the nitrogen compound is urea and, the nitrate salt is selected from Sodium Nitrate, Magnesium Nitrate and a combination thereof.

Further, in a preferred embodiment, the said salt mixture includes ammonium oxalate in 30 weight percent, nitrogen compound is 30 weight percent, Sodium Nitrate is 30 weight percent, and Magnesium Nitrate is 10 weight percent.

Further, in another embodiment, the said salt mixture includes oxalic acid.

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.

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 = 2 h.

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))/(Amount of scales taken)*100

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%), the 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 O2 atmosphere keeping 10 °C ramp per minute and kept for 2 hours.

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

Table 2: Offline descaling efficiency of different dry descaling salt formulations
S. No. Formulation (Wt.%) Initial weight taken (gm) Residual weight (gm) Offline Descaling efficiency (%)
1 Formic Acid-100% 40.35 40.10 62.91
2 Acetic Acid-100% 36.034 35.76 65.71
3 Sodium Hydroxide-100% 19.24 19.16 19.00
4 Sodium Carbonate-100% 15.10 15.00 26.00
5 Sodium Carbonate -30% + Potassium Carbonate-70% 36.68 36.78 26.91
6 Sodium Carbonate -23% + Potassium Carbonate -77% 36.10 35.96 35
7 Potassium Carbonate -100% 48.41 48.25 39
8 EDTA-100% 40.36 40.09 69.92
9 Ammonium EDTA-100% 48.31 48.04 67.46
10 Ammonium EDTA-35% + A1-M5 65% 18.92 18.69 59
11 Ammonium EDTA-50% + OA-50% 15.06 14.77 68.91
12 Ammonium EDTA-90% + Oxalic Acid-10% 35.96 35.69 67.77
13 Ammonium EDTA-90% + Ammonium Oxalate-5% + Solar Salt-5% 26.83 26.43 65
14 Ammonium EDTA-33.33% + Ammonium Oxalate -33.33% + Solar Salt- 33.33% 40.54 40.21 55.41

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
S. No Concentration Offline Descaling efficiency (%) Concentration Solubility pH
1 Sodium Hydroxide (100%) 19 5% YES 12.5
2 Sodium Carbonate-(100%) 26 5% YES 11.2
3 Sodium Carbonate -(30%)
Potassium Carbonate -(70%) 26.9 5% YES 11.0
4 Sodium Carbonate -23%, Potassium Carbonate -(77%) 35.0 5% YES 10.4
5 Potassium Carbonate -(100%) 39.0 5% YES 11.2
6 EDTA-100% 69.9 5% NO --
7 Ammonium EDTA-100% 67.5 5% YES 4.6
8 Ammonium EDTA-35% , A1-M5-65% 59.0 5% YES 5.5
9 Ammonium EDTA-50%+ Oxalic acid-50% 68.9 5% Partially 3.6
10 Ammonium EDTA-90%+ Oxalic acid-10% 67.7 5% Partially 7.0
11 Ammonium EDTA-90%+ Ammonium Oxalate-5%, Solar salt-5% 65.0 5% YES 5.9
12 Ammonium EDTA-33.33%+ Ammonium Oxalate-33.33%, Solar salt-33.33% 55.4 5% YES 6.6

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 shows acceptable pH and solubility. It is observed that EDTA-100% is not soluble in water and hence the pH cannot be detected.

Elemental analysis of scales before and after treatment with the selected descaling formulations
Further, it is observed that the formulation containing EDTA-100% is not soluble in water and have shown better descaling abilities. Further, it is observed that the formulation containing the Ammonium EDTA-100% are soluble in water and have shown better descaling abilities, i.e., formulation containing Ammonium EDTA-50% and Oxalic acid-50%, formulation containing Ammonium EDTA-90% and Oxalic acid-10%, formulation containing Ammonium EDTA-90% and Ammonium Oxalate-5% and Solar salt-5%. The descaling formulations which have shown better descaling abilities for them metal and hydrocarbon removal analysis before and after treatment was done, especially for EDTA and Ammonium EDTA. In this analysis it can be noticed that the formulation is effective in removing both metals and hydrocarbons effectively. Tabular representation for the same is provided in below Table-4.
Table 4: Elemental Analysis of Scales Before and After Treatment
Sample name Al
% Fe
% Ni
% Si
% V
% C
% H
% S
% O
% TOTAL CONTENT
Scale M 3.8 4.0 9.7 18.0 2.7 ND 1.7 12.7 42.4 94.1
EDTA 0.5 2.7 4.6 2.8 1.1 ND ND 1.0 23.0 35.7
Ammonium EDTA 0.2 2.0 3.5 5.0 1.2 ND ND 0.7 21.0 33.6

The descaling formulations that have shown better descaling abilities for them metal and hydrocarbon removal analysis before and after treatment was done. In this analysis it can be noticed that the EDTA is effective in removing both metals and hydrocarbons and EDTA is not soluble in water thus can act as an effective anti-fouling component.

From the above study and results of table 2-4, different descaling formulations have been selected and prepared which are tabulated in below table 5.

Dry Powder Descaling Salt
The table-15 shows list of powder descaling formulation with their offline descaling efficiency. It can be concluded that all the developed formulations are showing better offline descaling efficiency. To find out the thermal properties, residual mass at 800 °C and decomposition temperature of the formulations, TGA studies were carried out and the data was analyzed.

Table 5: Offline descaling efficiency of dry powder descaling formulations
S. No. Formulation (Wt.%) Initial weight taken (gm) Residual weight (gm) Offline descaling efficiency (%)
1 Magnesium Nitrate-10%, Sodium Nitrate-30%, Urea-30%, Ammonium Oxalate-30% 19.77 19.18 60.12
19.02 18.78 59.80
2 Magnesium Nitrate-70%, Urea-5%, EDTA-10%, Sodium Hydroxide-15% 48.35 48.14 51.25
3 Magnesium Nitrate-70%, Urea-5%,
EDTA-15%, Sodium Hydroxide-10% 15.33 15.08 63.65
18.96 18.69 66.00
4 Mg(NO3)2-10%, NaNO3-30%, Urea (30%), Ammonium Oxalate(30%)-50%, Oxalic Acid-50% 19.00 18.73 69.25
36.04 35.76 67.78
5 EDTA-33.33%, A5-M1-33.33%, Potassium Carbonate-33.33% 15.10 14.87 57.48
6 EDTA- 90%, Potassium Carbonate -10% 48.29 48.03 65.53
7 EDTA-90%, Ammonium Oxalate -5%, Solar Salt- 5% 40.37 40.09 69.92
8 Ammonium EDTA-100% 48.31 48.05 67.46
9 Ammonium Oxalate-100% 15.06 14.79 67.85
10 Urea-100% 26.66 26.39 66.72

Elemental Analysis before and after treatment of scales
To find out what percentage of metals, carbon, hydrogen, sulphur, oxygen and nitrogen have been removed by the dry descaling formulations, ICP-OES (metal analysis) and C, H, N, S, O (hydrocarbon) studies were carried out. The data for the same is shown below in table 6. The formulations that have shown better descaling offline efficiency i.e., more than 65%, for those ICP-OES and CHNSO data is being collected and analyzed. The sample taken was treated scale with formulation (1:1) at 800 °C for 2 hours.

Table 6: Metal and C, H, N, S, O contents before and after treatment
Sample Name Formulation (Wt.%) Al% Fe% Ni% Si% V% C% H% S% O% Total Content (%)
Scale M 3.80 4.0 9.7 18.0 2.7 ND 1.7 12.7 42.4 94.10
A5-M1 Mg(NO3)2-10%, NaNO3-30%, Urea (30%), Ammonium Oxalate(30%) 0.08 0.6 0.02 17.9 0.005 ND 1.7 7.1 35.0 64.41
A5-M3 Mg(NO3)2-70%, Urea-5%, EDTA-15%,NaOH- 10% 0.02 3.5 4.9 11.3 1.7 ND ND 12.7 30.1 64.22
A5-M1-OA A5-M1-50%, Oxalic Acid-50% 0.05 4.0 6.9 14.8 2.0 ND ND 0.7 34.7 63.73
UA Urea-100% 0.60 3.1 4.4 3.7 1.1 ND ND 10.2 23.6 46.90
AO Ammonium Oxalate-100% 0.20 2.4 4.5 3.2 1.0 ND ND 10 23.1 45.10
EDTA-SS-AO EDTA, Solar Salt, Ammonium Oxalate 0.30 1.2 3.0 5.0 1.0 ND ND 1.0 23.0 37.50
Am-EDTA Ammonium- EDTA-100% 0.20 2.0 3.5 5.0 1.2 ND ND 0.7 21.0 33.60

Thermal stability studies of scale and descaling salt (1:1 ratio) mixtures
TGA studies were carried out for the best powder descaling formulations, showing efficiency of more than 65%, “A5-M1-OA, AM-EDTA, EDTA-SS-AO” with “Scale M” scales. Scale material and descaling salt are taken in 1:1 composition and compared with the thermal descaling ability of scale alone from 25-800 °C using TGA. The TGA profile for the formulations is given in figure 4. It can be concluded from the curve that the 100% scale is not even 50% decomposing at 800 °C whereas in case of 1:1 scale and formulation the residual mass is less than 40%. The data and plot are mentioned below in tabular form for different powder descaling formulations.

Table 7: Variation in Residual Mass with temperature for 1:1 scale and Descaling salt mixture compared with pure scales
Salt Name +Scale M TGA (Residual Weight Percentage)
25 °C 50 °C 100 °C 200 °C 400 °C 600°C 800°C
Scale M 99.75 98.0 97 81.54 67.95 65.65 65.11
A5-M1-OA: Mg(NO3)2 10%, NaNO3 30%, Urea (30%), Ammonium Oxalate (30%)Oxalate(30%) 99.77 98.22 90.02 61.20 43.057 37.10 35.12
AM-EDTA-Ammonium-EDTA 99.98 98.83 98.94 90.89 31.17 18.70 18.00
EDTA-SS-AO- EDTA- Solar Salt-Ammonium Oxalate 99.80 98.76 94.67 80.46 38.13 22.39 11.40

Variation of residual mass with temperature of descaling formulation (100%)
To find out decomposition temperature and residual mass of the descaling formulations till 800 °C under nitrogen atmosphere, TGA studies were carried out as shown in figure 5. It can be concluded that the descaling formulations are decomposing before 500 °C and are having very less residual mass (less than 15%) till 800 °C. From this data it can be assured that the scales will not leave any residue at this working condition and hence can serve the purpose of removing scales.

Table 8: TGA data for Powder Descaling Formulation
TEMPERATURE (°C) A5-M1-OA EDTA-SS-AO AM-EDTA
25 99.7 99.8 99.9
50 98.1 98.8 98.2
100 86.6 94.8 92.4
200 44.4 80.5 75.8
400 08.0 38.1 38.8
600 05.9 22.4 30.8
800 04.0 6.1 0.3

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 9: dry descaling Formulation with Composition and Efficiency
Formulation Code Efficiency (%) Composition
Formulation 3 Dry powder 69.92 EDTA-90% + Ammonium Oxalate-5% + Solar Salt- 5%

Abbreviations:
A5-M1-OA Mg(NO3)2-10%, NaNO3-30%, Urea (30%), Ammonium Oxalate(30%)O
EDTA-SS-AO EDTA, Solar Salt, Ammonium Oxalate
AM-EDTA Ammonium EDTA-100%
A5-M1 Mg(NO3)2-10%, NaNO3-30%, Urea (30%), Ammonium Oxalate(30%)
A5-M3 Mg(NO3)2-70%, Urea-5%, EDTA-15%,NaOH- 10%
A5-M1-OA A5-M1-50%, Oxalic Acid-50%
UA Urea-100%
AO Ammonium Oxalate-100%
EDTA-SS-AO EDTA, Solar Salt, Ammonium Oxalate
Am-EDTA Ammonium- EDTA-100%
IFS-ED Improved FurnOKare
UAO-R2 (80%), Ammonium Oxalate (20%)
UA0-R1 Urea (20%), Ammonium Oxalate (80%)