Performance evaluation of descaling heat exchangers using Glutamine and Hexamine inhibitors

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1 Performance evaluation of descaling heat exchangers using Glutamine and Hexamine inhibitors Afaq Hassan 1*, Shahid Mirza 2, Areej Javed 3 1 Department of Chemical Engineering, University of Faisalabad, Faisalabad 2 Department of Chemical Engineering, NFC Institute of Engineering and Fertilizer Research, Faisalabad 3 Department of Chemical Engineering, University of technology and Engineering, Lahore ARTICLE INFO *Corresponding Author: afaq.hassan@tuf.edu.pk DOI: /nijesr Keywords: Acid corrosion, inhibitor mechanism, corrosion ABSTRACT The effect of different acids on the scale removal from heat exchanger are investigated in this study. Different concentrations of the acids are studied resulting higher the concentration of acids higher the removal of the scale. The inhibition effect of different concentration the hexamine and glutamine are studied with weight loss method. The results show that inhibition efficiency increases by increasing the concentration of the inhibitors. Time of dissolution plays an important role in the efficiency of the acid and the inhibitors, higher the time of dissolution higher will be the efficiency. Theoretical calculations result 2.5 M HCl solution with 0.80 grams of glutamine at 2.5 hr time gives the best results of removal of scale. Comparison on the basis of temperature is also done in this study, higher the temperature of the acid the greater the dissolution rate of the scale. I. INTRODUCTION Boilers are designed to produce steam or heat water. About 83% of world electricity is produced by boilers. The scale can reduce the lifetime of the boiler and the working of the boiler. Other drawbacks of scale formation are an increase of cost, replacement of the boiler again and again, and a very high energy usage i.e. up to 25% [1]. In some worst scenarios, the pressure of boilers may raise and damage the working place if an accident occurs. Fouling tubes of internal condenser/boiler are unfavorable to heat transfer; therefore condensing efficiency of steam decreases, which may cause a lesser vacuum pressure (higher stress) and decreases the steam turbine operations. In intense conditions, bad vacuum situations inside the condensing unit could diminish electric generation efficiency by extra 50% [2]. Deposited salts decrease the thermal heat transfer efficiency and normally affects the operation of the tube because of overheating which may also bring about plugging fouling of the system [3]. The deposition of CaCO 3 is the main problem of many industrial operations. In many heat exchangers, scale deposits are used which behave as a thermal insulator, appreciably lowering the boiler efficiency at the same time as inflicting heating element to overheat, and may cause to early component breakdown. The flow rates of flowing compounds decrease because of scale canal. Aside from manufacturing units, daily life equipment s which are used in homes consisting of water geysers, solar collectors, and many another area also affected by deposition of scale. Formation of scale in these areas can drastically decrease the efficiency of equipment and life. Other results are service charges increase, regular replacement of equipment s and may consume high energy up to 25% [4]. Chemical inhibitors and also de-scalers are currently, the very capable manner to save from scaling. But this could be very expensive and have a bad effect on the environment [5-6]. The inhibitors consisting of hetero atoms like oxygen, nitrogen, sulfur, and phosphorus are experimental as very efficient rust controlling compounds. The efficiency of those inhibitors changes upon the density of electron which is around the heteroatoms, the wide variety of molecules having activated adsorption centers and their charge density, 1

2 size of the molecule, adsorption mode, metallic complexes that are formed [7]. Inhibitors used for scale are a third largest product in water treatment up till 2016 of worth $ 3.6 billion. Many types of inhibitors are studied in past for the corrosion removal. Many thiohydantoins were also used as inhibitors in past. Study based on 5, 5 diphenyl 2-thiohydantoin as an inhibitor was performed and results that inhibition rate decreasing by adding a greater amount of the 5, 5 diphenyl 2-thiohydantoin [8]. Bis-2, 6-(3, 5-dimethyl pyrazolyl) pyridine (DPP) with steel in HCl solution was studied by Ergun resulting this inhibitor to be an efficient one [15]. Cleaning the scale with the solvent i.e. different acids are used to clean the scale of different compositions. One of the best solvent used is hydrochloric acid. Mostly the scale contained the Fe 2O 3, CaCO 3, CaO, Al 2O 3, MgO and ZnO salt. II. MATERIALS AND METHODOLOGY The scale was collected from the Sitara Chemicals Industries PVT Limited. The experiments were performed in the lab of University of Gujrat, Pakistan. The scale samples were treated chemically in the laboratory. Five different acids were selected for this study i.e. hydrochloric acid (HCL), Acetic acid (CH 3COOH), Nitric acid (), Sulfuric acid () and Phosphoric acid (). Different molar concentration solution was prepared for all acids. Firstly 0.5 M HCl solution was taken in 250 ml conical flask. Then the scale was washed with acetone and weighted 5 grams of the scale was poured into the flask. The solution with the scale was left for one hour for descaling. After one hour the solution was filtered and the weight of the leftover scale was measured. The same sample was again examined for the1.5 and 2 hour immersion time to study the effect of the time on the dissolution rate %. The same method was repeated for all the acids. The rate of dissolution is termed by grams of scale dissolved per minute. The cleaning efficiency is a quantity that is measured by the proportion of scale that is dissolved, expressed as a percentage of the total amount of scale present. M loss Dissolution Rate % = 100 (1) M sample M loss = (Mass of sample) after treatment (Mass of sample) before treatment To observe the effect of inhibitors i.e. glutamine and hexamine, different concentrations of the inhibitors were used (0.2 grams, 0.4 grams, 0.6 grams and 0.8 grams). To the same amount of acid solution that was used for immersion, a time effect was selected and inhibitors were added and left the solution of hydrochloric acid and phosphoric acid for 1 hour to examine the change in the dissolution rate %. Effect of temperature was also studied by the heating the sample up to 65 degree Celsius. Safety measurements were made in the laboratory to eliminate the risk of an accident. Safety glasses and hand gloves were used to avoid an accident. III. RESULTS A. Effect of concentration and time Five concentrations of 0.5 M, 1 M, 1.5 M, 2 M and 2.5 M were studied for each acid. It was found that increasing the concentration of acid, scale removal % increases. Highest scale removal was observed for the HCL solution. Other acids show lower dissolution rate % as compared to HCl and H3PO4 acids. The increase in the scale removal with increasing acid concentration is due to the increase in concentration gradient between the bulk and the solid solution interface which increases the reaction rate of the acid with scale. Co n Table 1 Dissolution rate % of scale with different acids concentrations HCl HCl HCl H 3PO 4 1hr 1.5hr CH 3C OOH CH 3C OOH CH 3C OOH 2

3 Table. 1 shows the performance of all the acids, it is clear that hydrochloric acid appears the best one among all the acids for scale removal. The effect of time on scale removal was also observed. It was observed that the percentage of scale removal increases with reactions time at a constant concentration and temperature. At 2 hours of reaction time, HCL removes more than 70% scale, whereas phosphoric acid removes 65% scale. Increase in the reaction time causes the scale removal % to increase. Figure 1 Effect of concentration of acids on Dissolution rate % at different time (a) HCL (b) H3PO4 (c) HNO3 (d) CH3COOH (e) H2SO4 Fig. 1. shows the effect of different acids concentration on the dissolution rate % of the scale under the condition of 1, 1.5 and 2hr. Experimental results show that 2.5 M solution at 2 hour immersion time gives higher dissolution rate% for all the acids as compared to the results obtained at a lower concentration of acids and at 1 hour dissolution time. 3

4 The overall efficiency of all the treated acids was lower than HCL efficiency under same experimental conditions. shows a very rapid increase in the dissolution rate % at low concentrations of almost 17% but at higher concentrations, the results are almost same at all time periods. Thus using this acid at lower concentration give a significant change in the result but at high concentrations, the results were not significant. shows a very low dissolution rate at all the concentrations as shown in Fig. 1. Time also has a negligible effect on all concentrations thus giving the low dissolution rate even after 2 hours. CH 3COOH offer 26% dissolution at 0.5 concentrations that is very low with respect to other acids. At higher concentrations of acid, immersion time does not affect the rate of dissolution only 1.1% increase is recorded at 2 hours and 0.8% at 1.5 hours. HCl offers highest dissolution rate among all the acids i.e. 92.4% at 2.5 M concentration at 2 hour immersion time. The lowest rates % were obtained from at all the concentrations. serve as a blanket to the entire metal surface with a protective layer of the compound used; this occurs as simple adsorption of the inhibitor ion on the metal surface. Different concentrations of inhibitors were used i.e. 0.2, 0.4, 0.6 and 0.8 grams to calculate the dissolution rate % in HCl and. Adding inhibitors to the acids results in an increase in dissolution rate %. Higher the concentration of the inhibitors used, higher dissolution rat % was recorded. The results obtained from the hexamine inhibitor in HCl are almost same with the result obtained for 2 hour immersion time thus saving the extra time of immersion. Glutamine serves to be a more efficient inhibitor in comparison to the hexamine. Glutamine offers more dissolution rate % at 1 Hour immersion time than that obtained from the 2-hour immersion without inhibitor. Fig. 2 shows the comparison of the inhibitors added in the acids. Glutamine in case of 2.5 M HCl results in 99.7 % dissolution rate at 1 hour time. B. Effect of inhibitors Adding an inhibitor to the acids is essential to diminish its corrosive effect on metals. Inhibitors Figure 2 Effect of inhibitors on Dissolution rate % (a) Hexamine in HCl (b) Glutamine in HCl (c) Hexamine in H3PO4 (d) Glutamine in H3PO4 4

5 C. Effect of temperature Increase in temperature imparts kinetic energy to molecules causing them to move faster and collide with more frequency and causing the rate of reaction to increase, this may be due to the effective penetration Table 6 Effect of temperature on Dissolution rate % of acids at high temperature to the internal structure of the scale. The reaction rate increases as the temperature increases, and has its maximum value at the highest temperature. Temperature 25 C and 65 C have been used for this study. Acid con HCL HCL 25 ºC 25ºC 25 ºC CH 3COOH CH 3COOH 25 ºC 25 ºC Figure 9 Effect of temperature on the Dissolution rate % for (a) HCL (b) (c) (d) CH 3COOH (e) 5

6 Figure 9 shows the effect of temperature on the scale removal process for all the acids. It was observed that the higher the temperature the better the percentage of scale removal when other conditions of the process (time, concentration) remained constant. HCl at 2.5 M concentration shows about 7% increase at 65 C. At lower concentration of acid, the effect of temperature is almost negligible for HCl acid. In case of nitric acid the rate increases at lower concentrations only, acetic acid does not shows any remarkable change at. IV. CONCLUSIONS This work explore the significance of inhibitors for descaling of heat exchangers. The principle method for the study was to immerse sample in acids with or without inhibitors to study the dissolution rate % for each acid. Increasing the concentration of acid the dissolution rate% increases. HCl > > > CH 3COOH > is the order of the acid for descaling heat exchanger. HCL provide maximum dissolution rate % among all the acids. is not recommended for the use for descaling as its scale removal power is very low even at high concentration and immersion time. This work shows that increasing the concentration of the acid, higher will be the dissolution rate %. Inhibitors offer high scale removal in less time, Glutamine offers better results than hexamine inhibitor. HCl in hexamine and glutamine shows 97.8% and 99.7% rate respectively with 1 hour immersion time and at 2.5 M concentration. Immersion time will be reduced by adding inhibitors. Increase in temperature shows an increases in the dissolution rate % i.e. for HCl at 25ºC the rate was 84% while at 65ºC it was 91%. ACKNOWLEDGMENT The authors acknowledge Sitara Chemicals Industries PVT Limited, who was the greatest source of help their efforts and valuable suggestions are truly commendable. The financial support and analytical facilities provided by the university of Gujrat Pakistan. The cooperation of Sitara Chemicals Industries PVT Limited is also acknowledged. REFERENCES [1] Schmitt G., et al. (2009). Global Needs for Knowledge Dissemination, Research, and Development in Materials Deterioration and Corrosion Control. World Corrosion Organization. [2] A. Ongun Yüce, G. Kardaş, Adsorption and inhibition effect of 2-thiohydantoin on mild steel corrosion in 0.1 M HCl, Corros. Sci. 58 (2012) [3] S. Deng, X. Li, X. Xie, Hydroxymethyl urea and 1, 3-bis (Hydroxymethyl) urea as corrosion inhibitors for steel in HCl solution, Corros. Sci. 80 (2014) [4] DOE, Energy Savers: Tips on Saving Money & Energy at Home, US Department of Energy, Office of Energy Efficiency and Renewable Energy (2011)1 44 [5] D. Hasson, H.Shemer, A.Sher, State of the art of friendly green scale control inhibitors: are view article, Ind.Eng.Chem.Res.50 (12) (2011) [6] X. Li, S. Deng, H. Fu, X. Xie, Synergistic inhibition effects of bamboo leaf extract/ major components and iodide ion on the corrosion of steel in H3PO4 solution, Corros. Sci. 78 (2014) [7] M. A. Qureshi, A. Singh, V. K. Singh, D. K. Yadav, A. K. Singh, Mater. Chem. Phys. 122 (2010) 114. [8] Ayşe Ongun Yüce, Esra Telli, Başak Doğru Mert, Gülfeza Kardaş, Birgül Yazıcı, Experimental and quantum chemical studies on corrosion inhibition effect of 5,5 diphenyl 2- thiohydantoin on mild steel in HCl solution, Journal of Molecular Liquids 218 (2016) [9] Chen, H. (2005). Research of high scale inhibitor in boiler water treatment. Master's thesis, Tianjin University, Tianjin [10] K. Anthony Selby, "Determining the Need for Chemically Cleaning a Boiler," International Water Conference, paper no. IWC-00-32, Pittsburgh, [11] Mel J. Esmacher and George H. Bodman, "Use of Comprehensive Deposit Analysis Techniques to Evaluate Boiler Deposits Prior to Chemical Cleaning," International Water Conference, paper no. IWC-00-33, Pittsburgh, [12] M. Suleman Tahir, Mahmood Salem, Experimental Study of Chemical De-scaling-I: Effect of Acid Concentration, Journal of Faculty of Engineering & Technology, , pages, 1-9 [13] K.R. Ansari, M.A. Quraishi, Ambrish Singh, Schiff's base of pyridyl substituted triazoles as new and effective corrosion inhibitors for mild steel in hydrochloric acid solution, Corros. Sci. 79 (2014) [14] A. Khamis, M.M. Saleh, M.I. Awad, B.E. El-Anadouti, Enhancing the inhibition action of cationic surfactant with sodium halides for mild steel in 0.5 M H2SO4, Corros. Sci. 74 (2013) [15] Ü. Ergun, D. Yüzer, K.C. Emregül, The inhibitory effect of bis-2, 6-(3,5- dimethyl pyrazolyl)pyridine on the corrosion behavior of mild steel in HCl solution, Mater. Chem. Phys. 109 (2008)