This article was downloaded by: [University of Calgary] On: 24 June 2015, At: 16:25 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Petroleum Science and Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lpet20 A General Correlation for Accurate Prediction of the Dew Points of Acidic Combustion Gases in Petroleum Industry B. ZareNezhad a a Faculty of Chemical, Petroleum and Gas Engineering, Semnan University, Semnan, Iran Published online: 04 Jun 2014. Click for updates To cite this article: B. ZareNezhad (2014) A General Correlation for Accurate Prediction of the Dew Points of Acidic Combustion Gases in Petroleum Industry, Petroleum Science and Technology, 32:16, 1988-1995, DOI: 10.1080/10916466.2012.730596 To link to this article: http://dx.doi.org/10.1080/10916466.2012.730596 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & com/page/termsand-conditions .tandfonline.Downloaded by [University of Calgary] at 16:25 24 June 2015 Conditions of access and use can be found at http://www. 2014 C Taylor & Francis Group. Dew point temperature is a function of the water vapor concentration and the concentration of acid species in the flue gas (Blanco and Pe˜na. At temperatures between 72 and 136◦ C. Petroleum and Gas Engineering. Iran A general correlation has been proposed for the first time for accurate prediction of the acidic combustion gases dew points to mitigate the corrosion potential in pollution control and energy recovery equipments.2012. SO2 . Semnan University. Address correspondence to B. HCl. the HCl condensation is also an important influencing factor regarding corrosion failure. Semnan University. Semnan. HBr. H2 O = 30 vol%). E-mail: Prof. The most important acidic gases. NO2 . Improvement of the thermal efficiency of flue gas treatment equipment may need further cooling to a temperature as low as 72◦ C.730596 A General Correlation for Accurate Prediction of the Dew Points of Acidic Combustion Gases in Petroleum Industry B. gas cooling below this dew point by radiation or convection forms a mist of corrosive acid droplets that is highly detrimental to the stack and heat recovery equipment (Cherif et al. HCl. PO Box 35195–363. the H2 SO4 condensation is the main cause of steel corrosion failure. are considered in this investigation. the H2 SO4 and HCl dew points are about 136 and 72◦ C. Faculty of Chemical. SO2 . These conditions can increase the potential for corrosion of the low temperature gas-path components (Lins and Guimaraes. combustion gas. and HBr. HCl = 300 ppmv.1080/10916466.com 1988 . At flue gas temperatures below 72◦ C. Keywords: acid dew point. SO3 .. LLC Copyright ISSN: 1091-6466 print / 1532-2459 online DOI: 10. This kind of corrosion differs from general atmospheric corrosion and causes heavy corrosion not only of ordinary steels but even stainless steels (Rockel and Bender. namely. 2008). For a typical flue gas (SO3 = 3 ppmv. INTRODUCTION Acid dew point corrosion results from condensation of flue gas acid species on low temperature gaspath surfaces. 2007) Sulfuric acid and hydrochloric acid dew point corrosion occur in flue gas treatment systems of waste incineration facilities. as well as hydraulic cement composites.Petroleum Science and Technology. NO2 .zarenezhad@gmail. energy recovery 1. and H2 O. 32:1988–1995. 2008).b. ZareNezhad. The condensed acids are corrosive to steel and almost all plastics. Semnan. 2002). Corrosion failures often occur because of condensing flue gasses containing SO3 . respectively. ZareNezhad1 1 Downloaded by [University of Calgary] at 16:25 24 June 2015 Faculty of Chemical. Many of the processes for improving the thermal efficiency of combined cycle plants can also result in lower flue gas temperatures leaving the heat recovery steam generators or increased flue gas moisture content. correlation. Petroleum and Gas Engineering. Acidic combustion gases can cause rapid corrosion when they condense on the surfaces of the heat recovery and flue gas treatment equipments. Iran. Further. corrosion. The presented correlation can be used for accurate prediction of the flue gas acid dew point temperatures over wide ranges of acid and water vapor concentrations in oil and gas industries. Kiang (1981) proposed different correlations for estimating the NO2 . To overcome this shortcoming. . It should be noted that the parameters Ai . 1999. A set of 940 dew point temperatures is determined for the most important acidic gases namely. The parameter.ACCURATE PREDICTION OF ACID DEW POINTS 1989 The following correlation (Verhoff and Banchero. the predicted dew points are usually 4◦ C low. NO2 .B] correlation) does not apply to halogenated or nitrated acid gases. 1974) was provided for predicting flue gas sulfuric acid dew point: Downloaded by [University of Calgary] at 16:25 24 June 2015 (1) where TDew is the sulfuric acid dew point in K and the partial pressures (pSO3 and pH2O ) are in mm Hg. λ and molecular weight. SO3 . Ci . 2004. and Di are not dependent on acid species and are always fixed. Although this correlation is more accurate at H2 O concentrations higher than 25%. Also in the range of 100–121◦ C. ◦ PROPOSED CORRELATION In this work. The previous correlation (the Verhoff and Banchero [V. Okkes (1987) proposed a correlation to overcome some of these shortcomings. Bi .. Gmehling et al. Nippon Oil Company. Dew points predicted in the range of 120–140◦ C have a positive deviation of 4◦ C and more. Mw are given for the relevant condensed acid. However there are usually significant deviations between predicted and experimental dew points over the concentrations prevailing in combustion gases. SO2 . 2001. Since the above correlations are not accurate enough for proper design of combustion equipments and heat recovery systems. HCl. but it significantly underpredicts the sulfuric acid dew points at low H2 O concentrations prevailing in oil and gas industries. which can be written as follows: (2) Where the partial pressures are expressed in atmosphere and the sulfuric acid dew point is in C. HCl and HBr dew points. The optimum values of all parameters determined by the genetic algorithm (Goldberg. 2008). 2007) are displayed in Table 1. Studies have found that the following general correlation can be used for accurate prediction of the dew points of acidic combustion gases: (3) where TDew is the acid dew point in ◦ C and the partial pressures (pAcid and pH2O ) are expressed in mm Hg. a general correlation based on all verified experimental data is proposed for accurate prediction of flue gas acid dew points. Ullmann’s. and HBr by using the most accurate vapor-liquid equilibrium data (Perry et al. It should be noted that there are some disagreements between the experimental data and the Verhoff and Banchero (1974) correlation especially at low acid concentrations and high H2 O contents. a general correlation has been presented for accurate prediction of the most important acid gases dew points. effect of vapor H2 O on sulfuric acid dew point FIGURE 1 Comparison of the proposed correlation with experimental sulfuric acid dew points at different moisture and acid concentrations.365 18. sulfur dioxide.011283 98.9 i=4 770.466 0. (3) Condensed Acids Downloaded by [University of Calgary] at 16:25 24 June 2015 λ Mw Indices A B C D H2 SO4 H2 SO3 HNO3 HCl HBr 0. However.165 Equation (3) with the parameters displayed in Table 1 yields the smallest sum of the squared errors for the whole range of acid dew point temperatures.57 4.622 −0. RESULTS AND DISCUSSION Predicted flue gas sulfuric acid dew points by using the proposed correlation (Eq. This condensation occurs on surfaces that are at or below the dew point of the acid gas.0 i=1 −45.88 31.4 −34. the acid dew point is very sensitive to the flue gas SO3 concentration such that a small increase in SO3 concentration leads to a significant increase in sulfuric acid dew point at a given H2 O concentration. ZARENEZHAD TABLE 1 The Optimum Values of Parameters in Eq. [3]) are compared with experimental data at different acid and moisture concentrations in Figure 1.04165 36. as the moisture concentration is increased.01 65.1990 B. .96 −0.4 −1. As shown in Figure 1.5 i=3 372. Whenever fossil fuels containing sulfur are fired in heaters or boilers.95 −2. The moisture content is also an important influencing parameter.93 −0.1 3.4365 0.00614 63. and to a small extent sulfur trioxide are formed in addition to carbon dioxide and water vapor.00466 80.1829 −0.0 i=2 −1320 138 −115.2 −78.005164 82. The performance of the proposed correlation is elaborated in the following section.0 i=0 160.031 −7. The SO3 combines with water vapor in the flue gas to form sulfuric acid and condenses on heat transfer surfaces that could lead to corrosion and destruction of the surfaces.9925 0. Since the sulfurous acid is always formed through the dissolution of SO2 in condensed water below the water dew point. . the corrosion risk in the waste heat recovery system is too high. As shown. the sulfurous acid condensation temperature is mainly influenced by the water vapor concentration. the vapor phase sulfur trioxide concentration has a very strong influence on flue gas dew point especially at SO3 concentrations below 100 ppmv. which is formed through the reaction of SO3 and H2 O in the flue gas.Downloaded by [University of Calgary] at 16:25 24 June 2015 ACCURATE PREDICTION OF ACID DEW POINTS 1991 FIGURE 2 Comparison of the proposed correlation with experimental sulfurous acid dew points at different moisture and acid concentrations. is usually condensed at relatively high temperatures. The trend of dew point variation with respect to the FIGURE 3 Comparison of the proposed correlation with experimental nitric acid dew points at different moisture and acid concentrations. the corrosion risk in the stack is lower as compared to the case of sulfuric acid. Since the sulfuric acid. Predicted and measured flue gas sulfurous acid dew points are compared in Figure 2. In most installations the formation of sulfuric acid is prevented by keeping the temperature above the sulfuric acid dew point as well as possible. is gradually reduced. However the sulfurous acid formation at the temperatures around 60◦ C speeds up the metallic corrosion in heat recovery systems. Thus the accurate prediction of sulfuric acid dew points at low SO3 concentrations prevailing in process industries is very important to control the corrosion problems in thermal waste treatment plants and energy recovery equipments. As shown in this figure. . the inlet temperature is at least 70◦ C. In a gas. Predicted flue gas nitric acid dew points by using the proposed correlation are compared with experimental data at different acid and moisture concentrations in Figure 3. containing 50 ppmv NO2 and 5 vol% water (a typical high NO2 containing GT gas) the NO2 dew point (28◦ C) is lower than the water dew point (33◦ C). According to Figure 2. In this case. The NO2 condenses as nitric acid below the nitric acid dew point or it dissolves in the condensed water below the water dew point to form nitric acid solution causing very severe stress corrosion cracking.Downloaded by [University of Calgary] at 16:25 24 June 2015 1992 B. which excludes water and nitric acid condensing. During operation of the Heat-Recovery Steam Generators (HRSGs). ZARENEZHAD FIGURE 4 Comparison of the proposed correlation with experimental hydrochloric acid dew points at different moisture and acid concentrations. the sulfurous acid dew point temperature is always below 70◦ C as long as the moisture concentration is not higher than 30 vol%. the NO2 dew point is usually higher than water dew point such that the nitric acid condensation takes place directly from the gas phase below the nitric FIGURE 5 Comparison of the proposed correlation with experimental hydrobromic acid dew points at different moisture and acid concentrations. At high flue gas NO2 concentrations. nitric acid can be formed by solving of the gas in the water droplets. moisture content is similar to the case of sulfuric acid such that the H2 O content is less influential at higher moisture concentration. only during shutdowns. B) and Okkes correlations and experimental data. in addition to sulfuric acid. effect of H2 O concentration on acid dew point is more important at low moisture concentrations as shown in Figures 4 and 5. In municipal solid waste fired plants. the flue gas hydrochloric and hydrobromic acid dew points are usually below 80◦ C in most practical cases. [1]) and Okkes (Eq. one has to deal with hydrochloric and hydrobromic acid formation.Downloaded by [University of Calgary] at 16:25 24 June 2015 ACCURATE PREDICTION OF ACID DEW POINTS 1993 FIGURE 6 Comparison of the proposed correlation with Verhoff and Banchero (V. Predicted results are in good agreement with experimental data as shown in Figures 4 and 5. acid dew point. respectively. According to these figures. . Predicted nitric acid dew points are in good agreement with the experimental data as shown in Figure 3. [3]) is compared with the V.B (Eq. The proposed correlation (Eq. Predicted flue gas hydrochloric and hydrobromic acid dew points by using the proposed correlation are also compared with measured data at different acid and moisture concentrations in Figures 4 and 5. [2]) correlations regarding the prediction of sulfuric acid dew points at a moisture concentration of FIGURE 7 Comparison between the proposed correlation predictions with the experimental acid gases dew points. Similar to the previous cases. Also the halogenated compounds used in various types of plastics are released in waste incinerators such that the dew point corrosion due to HCl or HBr condensation may take place. (2008). Therm... HCl and HBr respectively) on the surfaces of the heat recovery and flue gas treatment equipments. Optimization. Representation of VLE and liquid phase composition with an electrolyte model: application to H3 PO4 -H2 O and H2 SO4 -H2 O. H2 SO3 . Goldberg. The predicted flue gas acid dew points according to Eq.. and Machine Learning. F. 0. N. the Verhoff and Banchero correlation leads to a considerable acid dew point overprediction. Menke. Fluid Phase Equilib. E. and Pe˜na. Ammar.055%. and Fischer. On the contrary. K. 28:777–784. HCl and HBr) can cause rapid corrosion when they condense (as H2 SO4 .9994 respectively. CONCLUSIONS A general correlation has been presented for accurate prediction of the flue gas acidic dew points over wide ranges of moisture and acid gas concentrations. According to Figures 1–5. (3) is accurate enough for predicting the dew points of the different acid gases. The predicted flue gas acidic dew points are in excellent agreement with experimental data with the overall average absolute deviation of 1. M. Eng. M. J.5541%. M.). [3]) are much more accurate than those predicted by the V.Downloaded by [University of Calgary] at 16:25 24 June 2015 1994 B. Appl. ZARENEZHAD 20 vol% in Figure 6. ACKNOWLEDGMENTS The authors would like to thank the cooperation of National Iraninan Gas Company (NIGC) during the preparation of the manuscript. 194:729–738. The overall AAD%. (2007). (2002).B and Okkes correlations and are in excellent agreement with measured acid dew points as shown in Figure 6. SO2 . A. NO2 . W.. (2004). The accurate prediction of flue gas acid dew point is quite important for optimization of energy consumption in combustors and incinerators. which is small enough for design calculations. HNO3 . Cherif. In such a case the operator may incorrectly increase the air preheating level to combat the cold-end corrosion problem. 3) outperforms the other alternatives regarding the prediction of acid dew points in chemical process industries. The dew points predicted by the proposed correlation (Eq. Mgaidi. Genetic Algorithms in Search. and 0. J. (3) are also compared with all available experimental data regarding all aforementioned acid gases in Figure 7. Gmehling. In fact the sulfuric acid dew point temperature is the main bottleneck for increasing the performance of heat recovery systems. J. Azeotropic Data (2nd ed. D. The average absolute deviation (AAD%) in sulfuric acid dew point predictions is about 0. M. J. and F¨urst.9815. As shown in this figure. The proposed correlation (Eq. suggesting that Eq. As shown.. Acidic combustion gases (SO3 . 4.. The accurate prediction of flue gas acid dew point is quite important for optimum control of corrosion rate and energy consumption in combustors and incinerators. Berlin: Wiley-VCH. . the limiting dew point is that due to sulfuric acid and thus any heat transfer surface should be kept above H2 SO4 dew point if acid condensation is to be avoided.. it is important to predict the H2 SO4 condensation temperature accurately. Abderrabba. the proposed correlation can be used for accurate prediction of the flue gas acid dew point temperatures over wide ranges of moisture and acid gas concentrations.. Boston: Addison Wesley. RMSD and R2 values regarding the proposed correlation are about 1.055%. Increase in the boiler’s performance in terms of the acid dew point temperature: Environmental advantages of replacing fuels. REFERENCES Blanco. Since the sulfuric acid dew point is usually higher than that of the other acids. using the Okkes correlation leads to a significant dew point underprediction such that the air preheating level may not be adequate to overcome the corrosion risk. Krafczyk. (2001). D.. SO2 . Indust. ppmv yNO2 yHCl yHBr RMSD AAD% R2-value i Ai . Ullmann’s. ppmv concentration of HCl in the flue gas. (2008). (1987).. Tokyo. F. C. ppmv root mean square deviation percent of average absolute deviation correlation coefficient index (from 0 to 4) in Eq. ppmv concentration of SO2 in the flue gas. M. Verhoff. Di and λ Mw concentration of NO2 in the flue gas. Loss Prevention Proc. (1999). (1981). (3) parameters defined in Eq. Sulfuric acid dew point measurement. Japan. NO2 . Chem. J.◦ C partial pressure of H2 O in the flue gas. E. H. Chemical Engineers Handbook (7th ed. T. R. 70:71–72. HCl. G. Nippon Oil Company. A. Corrosion Handbook.). New York: Wiley. Get acid dew point of flue gas. Failure of a heat exchanger generated by an excess of SO2 and H2 S in the Sulfur Recovery Unit of a petroleum refinery. (2008). J. Process. 9:127–128. Okkes. Y. Bi . 7:53–55. (1974). mm Hg partial pressure of acid gas (SO3 . Predicting dew points of acid gasses. (3) molecular weight . M. and Maloney. Perry. Ullmann’s Encyclopedia of Industrial Chemistry (6th ed... ppmv concentration of HBr in the flue gas. (2007). mm Hg concentration of H2 O in the flue gas. Chem. B. Green. vol% concentration of SO3 in the flue gas. and Guimaraes. Germany: Society for Chemical Engineering and Biotechnology. Downloaded by [University of Calgary] at 16:25 24 June 2015 NOMENCLATURE TDew pH2O pSO3 pAcid gas yH2O ySO3 ySO2 sulfuric acid dew point temperature. mm Hg partial pressure of SO3 in the flue gas.ACCURATE PREDICTION OF ACID DEW POINTS 1995 Kiang. Eng. HBr). Rockel. J. Frankfurt. and Bender. and Banchero. Technical document. New York: McGraw-Hill. V. Prog. Eng. Predicting dew points of flue gases.. F. 20:91–97. R. H. H.). Ci . Lins. W. Hydrocarb. O.