Optimization Operational Variable of Bench Scale Biological Flue Gas Desulphurisation Application in Sulfuric Acid Industry

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1 World Applied Sciences Journal 18 (9): 11114, 1 ISSN IDOSI Publications, 1 DOI: 1.589/idosi.wasj Optimization Operational Variable of Bench Scale Biological Flue Gas Desulphurisation Application in Sulfuric Acid Industry 1 1, 4 Ricki M. Mulia, Haryoto Kusnoputranto, Setyo S Moersidik and Riwandi Sihombing 1 Environmental Science Study Program, Postgraduate Program, University of Indonesia Department of Environmental Health, Faculty of Public Health, University of Indonesia Department of Environmental Engineering, Faculty of Engineering, University of Indonesia 4 Department of Chemistry, Faculty of Mathematics and Natural Sciences, University of Indonesia Abstract: Flue gases from sulfuric acid industry mainly contain of Sulfur Dioxide (SO ) gas. One relatively new technology which might efficient to remove SO emission is Biological Flue Gas Desulphurisation. To investigate potential of BioFGD application in Sulfuric Acid Industry, research was conducted. Research was 1 conducted in Benchscale BioFGD consists of several unit operation which are absorption tank (R ), Sulfate reduction bioreactor (R ), Stripper (STR), HS gas Scrubber (R ) and regeneration bioreactor (R4). Performance evaluation to optimize BioFGD was conducted by preliminary simulation of operational variable. Optimum 1 condition in R1 occur when EBRT = 1 minute and mass loading.5 g.m.hour. Optimum condition in R 1 occur when HRT = hour, mass loading = 84 g.m.hour and nutrient flow rate = 1% of reactor volume/day. Optimum conditions in STR occur when air flow rate to STR is 4% of reactor volume/minute. Optimum 1 4 condition in R occur when mass loading =.155 g.m.hour. Optimum condition in R occur when 1 HRT = 4 hour, mass loading = 1 g.m.hour, air flow rate = % of reactor volume/hour and nutrient flow rate= 1% of reactor volume/day. Key word: Sulfuric acid industry SO gas emission BioFGD Operational variable. INTRODUCTION The biggest chemical product in the world is Sulphuric acid. Total Sulphuric acid product in the world is approximately 15 million ton. Flue gases from sulfuric acid industry mainly contain of Sulfur Dioxide (SO ) gas Unfortunately, there is no information concerning the application of BioFGD to remove SO emission from sulfuric acid industry. To investigate potential of BioFGD application in Sulfuric Acid Industry, research was conducted. [1]. There is a growth concern of SO emission due to its MATERIALS AND METHODS impact on environmental and health []. One relatively new technology which might efficient to remove Benchscale BioFGD. Benchscale BioFGD consists SO emission is Biological Flue Gas Desulphurisation of several unit operation which are absorption tank (R1) (BioFGD) []. with volume lt, Sulfate reduction bioreactor (R) with Nowadays commercial BioFGD has used in volume 1 lt, Stripper (STR) with volume 5 lt, HS gas Natural gas processing. On 1 September, Scrubber (R) with volume 1 lt and regeneration natural gas containing HS was introduced to the first bioreactor (R4) with volume lt. BioFGD was fed with highpressure ShellPaques unit at Bantri, east of flue gases from sulfuric acid industry. Figure 1. shows TM Calgary in Canada. The ShellPaques/THIOPAQ schematic of BioFGD installation. There are anaerobic process has been developed by Paques B.V. Shell microorganism in R and aerobic microorganism in R4. Global Solutions International BV and is a biological Simulation Variable. Several preliminary simulations process for removing HS from (high pressure) Natural were conducted. In order to investigate SO removal Gas [4]. efficiency, simulations of operational variable in R1 were Corresponding Author: Ricki M Mulia, Environmental Science Study Program, Postgraduate Program, University of Indonesia, Tel: , Fax:

2 World Appl. Sci. J., 18 (9): 11114, 1 Fig. 1: Bench scale BioFGD installation conducted. Performance of BioFGD not only HS + Fe (SO 4) FeSO 4+ HSO 4+ S () determines by operational variable in R1 but also determine by other unit operation (R, STR, R and R4). Elemental sulfur is removed from the solution by Hence, simulation of R, STR, R and R4 were sedimentation tank, while ferous sulfate (FeSO 4) solution conducted in addition on simulations of operational is led to R4 where Thiobacillus ferrooxidans oxidizes variables in R1. Simulations variable in R are Hydraulic ferous sulfate to ferric sulfate according to Eq. (4). Retention Time (HRT), mass loading and nutrient flow Finally, Ferric sulfate solution is led to R as HSgas rate. Simulation variable in STR is air flow rate to STR. absorbent. Simulation variable in R is mass loading. Simulations variable in R4 are HRT, mass loading, air flow rate and FeSO 4+ 1/O + HSO 4T. ferrooxidan Fe (SO 4) + HO nutrient flow rate. (4) RESULTS AND DISCUSSION BioFGD process starts by absorption SO emission and conversion into Sulfite (HSO ) in R1 according to Eq. (1). + SO + HO HSO + H (1) Due to the present of Oxygen (O ) in the flue gas, Sulfite is oxidized to Sulfate (SO ) according to Eq. (), 4 + HSO + ½ O SO 4 + H () In R, Sulfate is converted by Sulfatereducing bacteria (SRB) into Sulfide (HS ) under anaerobic condition, using Molasses (C6H1NNaOS) as electron donors. Sulfide is stripped off and transferred into HSgas in STR. HSgas is absorbed and oxidized to elemental sulfur (S ) with ferric sulfate in R according to Eq. () Investigation of SO removal efficiency was conducted by simulation R1 operational variables. Figure. shows the simulations of Empty Bed Residence Time (EBRT) in R1. Empty Bed Residence Time (EBRT) refers to the time of SO emission move from R1 inlet to R1 outlet. Results of EBRT reveals the optimum contact time between SO emission and absorbent (liquid phase). Maximum SO emission removal efficiency occur when EBRT 1 minute. If EBRT below 1 minute, SO emission move too fast in R1 and the contact time between SO emission and absorbent is too short. Hence, SO removal efficiency will decrease. When EBRT exceed 1 minute, SO emission move too slow in R1. It cause absorbent agglomerate occur, hence absorbent surface area decrease. When absorbent surface area decrease, removal efficiency decrease. Besides EBRT, absorbent pump pressure simulation in R1 was conducted. Figure. shows the simulations of absorbent pump pressure in R1. 111

3 World Appl. Sci. J., 18 (9): 11114, 1 EBRT vs. Efficiency 9 SO removal efficiency (%) Fig. : EBRT vs SO removal Efficiency EBRT (minute) Pressure vs. efficiency 1 9 6, SO Removal Efficiency (%) , 5 4, 7.75, 7.5 7, 4 8, 1.56 Pressure vs. efficiency Pump pressure (kg/cm ) Fig. : Absorbent pump pressure vs. SO removal efficiency 9 Mass Loading vs. Efficiency SO Removal Efficiency (%) Mass Loading (g.m.hour 1 ) Fig. 4: Mass Loading vs. SO removal efficiency 11

4 World Appl. Sci. J., 18 (9): 11114, 1 Table 1: Optimum operational variable of bench scale BioFGD Optimum value No. Variable R1 R STR R R4 1. EBRT 1 minute. Absorbent pump pressure 6 kg/cm. mass loading.5g 84g.155g 1g 4. HRT hour 4 hour 5. nutrient flow rate 1% of reactor volume/day 1% of reactor volume/day 6. Air flow rate 4% of reactor volume/minute % of reactor volume/hour Results of absorbent pump pressure in R1 reveals the optimum pressure to enlarge the absorbent surface area. Optimum removal efficiency achieve when optimum absorbent surface area occur. The curve reveals that SO gas removal efficiency increase by increasing absorbent pump pressure from kg/cm to 6 kg/cm. The increases of SO gas removal efficiency due to the increase of absorbent surface area. On the contrary, when absorbent pump pressure over 6kg/cm there is the possibility of absorbent move to fast hence the contact time between absorbent and SO gas too short. In addition to EBRT and absorbent pump pressure, mass loading simulation in R1 was conducted Figure 4. shows the simulations of mass loading in R1. Mass loading formula is shown in Eq.(5). Results of mass loading simulation reveals the optimum mass loading to reach the maximum removal efficiency. Q* C Mass Loading ( Volumetric) = i Vf Note: Q =. 1 Flowrate ( ) Ci = Feed concentration (gr.m ) Vf = Reactor Volume (m ) Moleculer trasfer in unit operation depent on concentration equilibrium between contaminant and absorbent liquid. Equilibrium is achieved in optimum mass loading. When mass loading exceed optimum value, removal efficiency will decrease due to limited absorption capacity [5]. By knowing the optimum mass loading, the design engineer can scale up to treat larger flow rate with a larger reactor volume [6]. Results of simulation operational variables for all unit operation are shown in Table 1. Results of HRT in R and R4 reveal the optimum contact time between substance and bacteria to reach the (5) maximum conversion of substance. Below the optimum value, the contact time between substance and bacteria is too short hence conversion decreases. When the optimum value exceed, the mixing is too slow hence the distribution of substance is bad. Bad distribution of contaminant reduce the contact between substance and bacteria, hence substance conversion will decreases [7]. Air flow rate in STR is needed to strip off Sulfide and transferred into HSgas. Optimum Air flow rate to STR is 4% of volume/minute. Below optimum air flow rate, the pressure is too low to strip off Sulfide and transferred into HSgas in STR. However if air flow rate to STR exceed 4% of volume/minute, liquid overflow from STR will occur. In addition, the more air flow rate to STR the more Oxygen dissolved which is able to oxidize HSgas from STR. Results of nutrient flow rate in R and R4 reveal the optimum flow rate of bacteria nutrient to support their growth in bioreactor. Below optimum value, bacteria growth is limited. When bacteria nutrient exceed the optimum value, overfeeding occur in R1 and R4. Overfeeding probably increase bacteria growth over the available space follows with decrease on bacteria activities [8]. R4 was inoculated with Thiobacillus ferrooxidans that lives on aerobic environment. It needs Oxygen to support its live. Oxygen is available by conducting air flow rate from compressor to R4. Optimum value of air flow rate in R4 reveals the optimum Oxygen (O ) need for optimum growth of microorganism in R4. CONCLUSION Research result shows us that performance of Bio FGD operation depend on operational variable. In order to optimize SO gas removal efficiency in sulfuric acid industry, BioFGD needs to operate in optimum operational variable. 11

5 World Appl. Sci. J., 18 (9): 11114, 1 ACKNOWLEDGMENTS 4. Elkanzi, E.M., 9. Simulation of the Process of Biological Removal of Hydrogen Sulfide from Gas. The authors sincerely thank Dr. Marnis Hendrison for Proceedings of the 1st Annual Gas Processing deep discussion during preliminary design of experiment. Symposium H. Alfadala, G.V. Rex Reklaitis and M.M. The authors wish to thank Prof. Dr. Ir. M. Nasikin M. Eng, ElHalwagi (Editors) 9 Elsevier B.V. Department Dr. Ir. Budi Darmadi MSc, Dr. Tri Edhi Budhi Soesilo and of Chemical Engineering, University of Bahrain. Dr.Ir. Hayati Iskandar MSc for their fruitful discussion of 5. Rulkens, W.H. and H. Bruning, Principles experimental result. of Environmental Technology: lecturenotes, Subdepartment of Environmental Technology, REFERENCES Wageningen University. 6. Devinny, J.S., M.A. DeShusses and T.S. Webster, 1. European Fertilizer Manufacturers Association/ Biofiltration for Air Pollution Control. New EFMA (n.d.). Production of sulphuric Acid. York: Lewis Publishers. Accessed 19 Mei Lettinga, G., L.W. Hulshoff Pol and G. Zeeman,.. Miller, T.G. and S. Spoolman, 8. Environmental Biological wastewater Treatment PartI Anaerobic Science (1th ed.), USA: Thomson Learning, Inc. Wastewater Treatment, lecture notes. The. Grootaerd, H., A.D.E. Smul and W. Verstraete, Netherlands: Wageningen University. Biological flue gas desulphurisation. Paper presented 8. Hendrick, D.B., B. Guckert and D.C. White, at Forum fo Applied Biotechnology, September, Gent, Starvation and overfeeding stress on microbial Belgium. activities in highsolids highyield methanogenic digester. Biomass and Bioenergy, 1():