Separation and Purification Technology 63 (2008) 86–91 Contents lists available at ScienceDirect Separation and Purification Technology journa l homepage: www.e lsev ier .com Pierced iox remova Lei Meng ing College of Envi a r t i c l Article history: Received 2 Jul Received in re Accepted 5 Ap Keywords: Desulfurizatio Jet bubble reac Pierced cylind Waste gas stre signi cylind ted a even nsive cial a 95% S com ion o drop within the tower increased from 1.5 kPa to 3kPa, and removal efficiency of SO2 increased from 50% to 95%. This gas inlet device overcame the problems of uneven distribution and short-circuiting of gas streamswithin a typical gas inlet device in a jet bubble reactor, and removal efficiency of SO2 by the tower was improved considerably. Clogging and scaling within the tower were also avoided. This type of gas inlet device is simple and effective for purification and treatment of waste gas streams. © 2008 Elsevier B.V. All rights reserved. 1. Introdu Distribu determine i streams oft attention h through gas Type an the distribu of gas inlets portion of crosses the tribution. A various kind enter a colu the column Recently formance o developme (SulzerBrot a very high ∗ Correspon E-mail add 1383-5866/$ – doi:10.1016/j.s ction tions and flow patterns of gas streams within a reactor ts purificationperformances. Unevendistributionof gas en results in low removal efficiency. Therefore, close as been paid to distributing gas streams more evenly distribution system within a reactor [1–4]. d structure of a gas inlet device can significantly affect tion of gas streams within a reactor. One common type is a straight inlet which is usually located in the lower a column and is below the supporting grid that only wall [5]. A straight inlet doesnot affect the initial gasdis- nother type of gas inlet is a circular inletwhere there are s of orifices. Through the orifices, incoming gas streams mn tangentially, and aredistributedmore evenlywithin [5,6]. , more innovations have been made to improve per- f gas inlet devices. One of these innovations is the nt of the Tangential Vane Gas Inlet Devices (TVGIDs) hers Ltd.,Winterthur, Switzerland)whichcanbeusedat gas velocity in the feed pipe of F-factors up to 120Pa1/2. ding author. Tel.: +86 731 882 3987; fax: +86 731 882 2829. ress:
[email protected] (C. Yang). Incoming gas stream flows radically around the vessel, and is dis- tributed by a TVGIDs. This type of inlet device is suitable for vessels whose inner diameter is larger than 4m, and uneven distribution of gas streams within the tower still exists. Another innovative grid inlet devices developed by Glitsch Inc. has the similar struc- ture as the TVGIDs except that there is one more gas distribution port mounted at the top of the device. Although this improvement leads to more even distribution of gas streams, it is more complex to install and operate the columns with this type of inlet devices [7]. Pierced cylindrical gas inlet device is different from tradi- tional distribution devices [8–11]. Gas streams are forced to enter the tower through injecting and bubbling, and the liquid is the continuous phase. Gas distribution, liquid agitation, and droplet eliminationoccur simultaneouslyafter gas streamsentereda tower, and gas distribution condition is dramatically improved, conse- quently, performances of an absorption tower are significantly enhanced [12,13]. Although many innovations have been made, development of new gas inlet devices is still needed. In this paper, the structure and principle of the pierced cylindrical gas inlet device for jet bub- bling reactors are described, hydraulic properties of the tower is evaluated, and the effect of pH value of the absorbent slurry on desulfurization efficiency is investigated. Performances of this gas inlet device are also compared with other types of gas inlet devices see front matter © 2008 Elsevier B.V. All rights reserved. eppur.2008.04.003 cylindrical gas inlet device for sulfur d l from waste gas streams , Chunping Yang ∗, Haiming Gan, Ting Wu, Guangm ronmental Science and Engineering, Hunan University, Changsha, Hunan 410082, China e i n f o y 2007 vised form 28 March 2008 ril 2008 n tor rical gas inlet device am a b s t r a c t Configuration of a gas inlet device can or separation. In this paper, a pierced perforatedwall and is tangentially loca slurry exists. Incoming gas streams are leaving the inlet device, therefore, inte phases mix completely, and the interfa Results show that the tower achieved about 3kPa for the entire tower, an in 2000m3/h. When the depth of immers / locate /seppur ide Zeng, Hong Chen, Sanxia Guo ficantly affect the performance of a tower for gas purification rical inlet device is investigated which consists of an evenly t the lower portion of a jet bubble reactor where an absorbent ly distributed into and flow through the absorbent slurry after agitation is resulted. Consequently, the gas, liquid, and solid rea for mass transfer within the tower increases dramatically. O2 removal and over 90% dust removal at a pressure drop of ing SO2 concentration of 0.12% (v/v) and a gas flux of about f the grid holes increased from 0mm to 100mm, the pressure L. Meng et al. / Separation and Purification Technology 63 (2008) 86–91 87 to present guidelines for its application in industrial area in the future. 2. Materials and methods 2.1. Design of tower The pierced cylindrical gas inlet device for jet bubble reactors consists of twocoaxial glass cylinderswhosediameters are 600mm and 800mm, respectively (Fig. 1). The outer cylinder is connected to the base of the tower, and the bottom of the inner cylinder is 0.5m higher than the base of the tower. At the lower portion of the inner cylinder, there are 177 quadrate sparger holes which are 5mm×100mm. The distance to the neighboring holes is 5mm. Fig. 1. Schema of the inlet dev (4) inside cylin (8) liquid disch The two cylinders form an annular chamber. At the top of the chamber, there are 78 cone-shaped holes whose upper and lower diameters are 3mm and 5mm, respectively. The holes are 10mm apart from e absorbent s holes. The g incoming g 190mm [12 2.2. Prepara The was air into whi using tapw When the li of tap wate Co., Changs flow to the 2.3. Proced Before o to a givenw absorbent s to feed the After th chamber be moving dow cylinder. Du from the top stage (Fig. 1 the inner cy level in the holes. Whe the absorbe lot of bubbl sively stirre the absorbe bling layer o transferpro the liquid a [15,16]. 2.4. Measur The inco outlet of the ization effic The pres manometer value was e Scientific In gas streams ults ects sure nd tw sed a alf o dhes id le than tic of the gas inlet device. (a) Idle state, (b) working state, (c) section ice. (1) Absorbent import, (2) annular chamber, (3) outside cylinder, der, (5) cone-shaped nozzle, (6) gas inlet, (7) gas distribution jets and arge port. 3. Res 3.1. Eff Pres rates a were u lower h using a the liqu higher ach other. When the tower is not operated, the level of lurry is about 300mmhigher than the topof the sparger as inlet is tangent with the outer cylinder. The pipe for as stream is made of PVC, and the inner diameter is ,13]. tion of waste gas streams and absorbent slurries te gas stream was synthesized using a stream of clean ch SO2 was added. The absorbent slurry was produced ater intowhich limeswas individually addedandmixed. me slurry was prepared, 5.0 kg CaO was added to 360L r. A blower (Model 9-19:4A, Changsha Blower Factory ha,Hunan,China)wasused to force thewastegas stream tower. ures for startup and operation of system peration, the tower was filled with the absorbent slurry ater level. Then, the pumpwas operated to circulate the lurry in the tower system. The air blowerwas turned on synthesized waste gas stream. e waste gas stream tangentially entered the annular tween the cylinders, it revolved in the chamber while nwards to the holes in the lower portion of the inner ring this period, the absorbent slurry was also sprayed of the annular chamber to result in the first absorption ). At the same time, the liquid was pushed down into linder by the gas flow, which resulted that the water chamber was 100–400mm lower than the top of the n the gas stream flowed through the holes and entered nt liquid in the inner cylinder at a rate of 5–20m/s, a es were produce, and the absorbent slurry was inten- d (Fig. 1) [12–15]. When the air bubble flowed through nt slurry in the inner cylinder and rose above the bub- ver the absorbent slurry consequently,multistagemass cesswas resulted.Due to the large contact areabetween nd gas phases, and mass transfer rate was very high ement of reactor performances ming gas flow, the pressure drop between the inlet and tower, pH value of the absorbent slurry, and desulfur- iency of the tower were measured. sure drop was measured by an YDM-1 digital micro- (Zhaoyuan Daming Measuring Appliance Co.). The pH xamined by the PHS-2C acidometer (Zhejiang Xiaoshan strument Co.) once every 3min. SO2 concentration in was analyzed using the standard method in China. and discussion of hole-size and gas flow rate on pressure drop drop of the tower was measured at various gas flow o sets of hole-size separately. Tap water and clean air s the absorbent andwaste gas stream, respectively. The f the holes in the wall of the inner cylinder was blocked ives to change hole-size. Before startup of the tower, vel in the tower was set at either as high as or 100mm the top of the holes in the wall of the inner cylinder. 88 L. Meng et al. / Separation and Purification Technology 63 (2008) 86–91 Fig. 2. Effect of gas flow rate on pressure drop of the tower. The lower half of the holes in the wall of the inner cylinder was blocked. (�) The depth of water level above the top of the holes was 100mm; (�) the depth of water level above the top of the holes was 0mm. The pressure drops of the tower weremeasured at various gas flow rates (Fig. 2). It can be seen from Fig. 2 that the pressure drop of the tower increasedwith an increased gas flow rate or an increased water level of the absorbent in the tower. Thehighest-pressuredrop was about 2.5 kPa in these experiments. The adhesive blocks in the holes were then removed to restore the full size tively set at holes in the the water le various gas also increas level of the about 1.8 kP From the in the wall gas flow rat 3.2. Effect o Perform were evalua solution asm tively. The h in this expe pH values o are listed in maintained higher than Fig. 3. Effects tower. The hol level above th of the holes w 100mm. Fig. 4. Effect pressure drop higher the s could achie value of the solution in also, becaus in the towe rform t rem 3/h, dard dust his t a la ctor eams uid p ases e ann a si ose towe hiev �m [ mpa t bub stalle ith ical part gas inlet, and there were eight sparger pipes in the lower of the holes. The water level in the tower was respec- 0mm, 50mm, or 100mm higher than the top of the wall of the inner cylinder before operation. At each of vel, pressure drops of the tower were measured at the flow rates (Fig. 3). Fig. 3 shows that the pressure drop edwith an increased gas flow rate or an increasedwater absorbent in the tower. The highest-pressure drop was a in these experiments. se experimental results it can be seen that the hole area of the inner cylinder, the water level, and the incoming e affected the pressure drop significantly. f pH value of absorbent on SO2 removal ances of the tower for purification of waste gas streams ted using a waste gas stream containing SO2 and limes odelwaste gas streamand absorbent solution, respec- oles in the wall of the inner cylinder were fully open riment. SO2 removal efficiency in the tower at various f the absorbent solution was measured, and the results Fig. 4. It can be seen from Fig. 4 that the tower stably high sulfur removal efficiency when the pH value was about 6. The higher the pressure drop of the tower, the 3.3. Pe Dus 2000m tal stan from in from t existed ble rea gas str the liq gas ph ple, th played cles wh in this only ac than 1 3.4. Co reactor A je and in paredw cylindr of two gential of gas flow rate and water level in the tower on pressure drop of the es in thewall of the inner cylinderwere fully open. (♦) Height ofwater e top of the holes was 0mm; (�) height of water level above the top as 50mm; (�) height of water level above the top of the holes was part (Fig. 5 the sparger tangentially then passed in the react 3.5. Compa pressure dro When w drop of the typical jet b When wate of pH value on sulfur removal. (�) Pressure drop was 2.62kPa; (�) was 3.04kPa; (�) pressure drop was 2.34kPa. ulfur removal efficiency. Therefore, this gas inlet device ve high desulfurization efficiency by controlling the pH absorbent solution, the water level of the absorbent the tower, and the gas inlet pressure of the tower. And e of the low pH value, the CaSO4 was not easy to knot r. ances of dust removal oval efficient reached above 98% at a gas flow rate of a pressure drop of about 3kPa. Therefore, environmen- s could be reached for the control of dust emissions rial or municipal waste gas streams. High dust removal ower is resulted from the following facts. First, there rge area of gas–liquid interfacial contact in the jet bub- using the tangential circular gas inlet device. Then, the were more evenly distributed when flowed through hase in the tower. Multi-stage contact of the liquid and also contributed to the high dust removal. For exam- ular chamber between the walls of the two cylinders milar role as a water-film dust remover. As for parti- diameter was below 1�m, the dust removal efficiency r was 60%. While a conventional spraying tower could e 20% dust removal for particles with a diameter less 17]. rison with typical gas inlet device for a jet bubble ble reactor with a typical gas inlet device was designed d in our laboratory whose performances were com- that of the jet bubble reactor equippedwith the pierced gas inlet device. This typical gas inlet device consisted s, the upper part was an annular chamber with tan- ). There were 24 orifices (100mm×5mm) in each of pipes.When a gas stream entered the annular chamber , it revolved downward along the annular chamber, and through the orifices before entering the liquid phase or. rison of relationships between gas flow rate and p under various operating conditions for two towers ater was not filled in these two towers, the pressure pierced cylindrical tower was higher than that of the ubble reactor at a similar operation condition (Fig. 6). r was filled in the towers, the pierced cylindrical tower L. Meng et al. / Separation and Purification Technology 63 (2008) 86–91 89 Fig. 5. Schematic of a jet bubble reactorwitha typical gas inletdevice. (a) Front view; (b) top view. (1) Gas inlet, (2) annular chamber for gas distribution, (3) sparger pipe, (4) support beam, (5) jets, (6) liquid discharge port and (7) tower wall. Fig. 6. Relationships between gas flow rate and pressure drop when water was not filled in the two jet bubble reactors. (�) Pierced cylindrical gas inlet device; (�) typical gas inlet device. Fig. 7. Relationships between gas flow rate and pressure dropwhenwaterwas filled in the two jet bubble reactors. (�) Pierced cylindrical gas inlet device; (�) typical gas inlet device. read a high than 1800m pressure dr (Fig. 7). Differen contribute t There were drical jet bu device for t hole area. T in the pier at a higher pierced cyl wall, which While this and operat of the towe SO2. 3.6. Compa height of jet The rela bling zone i from Fig. 8 reactor wit cantly highe operating c the pierced typical jet b and gas ph cients could pierced cyli Fig. 8. Relatio Pierced cylind er pressure drop when the gas flow rate was no more 3/h, and the typical jet bubble reactor read a higher op when the gas flow rate was no less than 2200m3/h t hole area and structure of the two-gas inlet devices o the relationships of pressure drop and gas flow rate. 174 holes in the gas inlet device for the pierced cylin- bble reactor, and there were 192 holes in the gas inlet he typical jet bubble reactor. Each hole has a similar here was a floating type pneumatic agitation device ced cylindrical tower, which consumed more energy gas flow rate. Due to the gas rotary motion in the indrical tower, the liquid was pushed onto the tower increased gas–fluid contact and energy consumption. pierced cylindrical jet bubble reactor was constructed ed at full-scale, the liquid film on the inner surface r wall could increase removal efficiencies of dust and rison of relationships between gas flow rate and bubbling zone tionships between gas flow rate and height of jet bub- n the two reactorswerepresented in Fig. 8. It canbe seen that the height of jet bubbling zone in the jet bubbling h the pierced cylindrical gas inlet device was signifi- r than that in the typical jet bubble reactor at a similar ondition. Therefore, the gas resident time in tower with cylindrical gas inlet device was larger than that in the ubble reactor, therefore, a better contact of the liquid ases, and consequently a higher mass transfer coeffi- be reached in the jet bubbling reactor installed the ndrical gas inlet device. nships between gas flow rate and height of jet bubbling zone. (�) rical jet bubble reactor; (�) typical jet bubble reactor. 90 L. Meng et al. / Separation and Purification Technology 63 (2008) 86–91 Fig. 9. Relatio drical gas inlet 3.7. Compa desulfurizat SO2 rem absorption Fig. 9 that d pH value fo stream was Zheng et al gas stream each openin [18] is much sparger pip mass transf 3.8. Advant The adv aspects. Fir ticulate pol easy to ope ple and ene the absorbe themovem mass transf zones for re scaling wer The pier tor had a si of Sulzer Co gas inlet de used a tang However, th tion device the devices device for j inlet device the disperse intensive ag tower throu scaling was bles, thegas distribution into a singl Therefore, l Howeve in a large- uneven [4,2 cylindrical unevenly, and the flow rate of gas passing through the zones neigh- boring the center of the cylinders was considerably less than that of gas flowing through the areas near the wall of the inner cylin- caus ransf to ap desu t. clus jet b ce ca gas p es fr d exc gas, l mixe . pres onab pilot inlet r gas mple ce. wled pro tion nt Ta (NCE edO a, an e Fou nces Kouri, (199 rtrova ked co ee, A. dups i . Porte . 32 (1 lujic, ssure arakc cess. 4 . Yu, C ing, C uan, W mns, nships of pH value and desulfurization efficiency. (♦) Pierced cylin- JBR; (�) JBR [18]. rison of relationships between pH value and ion efficiency oval efficiencies at different pH values in different towers are presented in Fig. 9 [18]. It can be seen from esulfurization efficiency increased with an increased r both the reactors. SO2 concentration in the coming gas about 2800mg/m3 (1000ppmv) in the experiments by . [18]. In this study, SO2 concentration in the incoming was about 7100mg/m3 (2500ppmv). However, area of g in the sparger pipes for the JBR used by Zheng et al. smaller than that for our reactor. Small opening in the es usually leads to small bubbles and consequently high er coefficients as well as high-pressure drop. ages and disadvantages antages of this gas inlet device included the following st, this device is effective to remove gaseous and par- lutants from waste gas streams. Second, this device is rate with little maintenance. At last, this device is sim- rgy saving. In this tower, intensive agitation and mix of nt slurrywith thewaste gas streamswere resulted from ent of the gas streams itself. Therefore, a high gas–liquid er rate was achieved, stirrers were not required, dead actions were diminished in the tower, and clogging and e avoided [15,19]. ced cylindrical gas inlet device for a jet bubble reac- milar structure to the Tangential Vane Gas Inlet Device rporation in Switzerland and the tangent annular grid vice of Glitsch Corporation in USA. All of these devices ential air inlet and an annular chamber configuration. e turning vanes as well as top-mounted gas distribu- s in the Sulzer and Glitsch Companies’ devices made more complicated [5]. This pierced cylindrical gas inlet et bubble reactor was different to the traditional gas der. Be mass t proper ers for presen 4. Con 1. The devi the rang coul 2. The and 98% 3. The reas 4. The gas othe is si nan Ackno This Founda Excelle China Return ofChin Scienc Refere [1] R.J. J. 61 [2] T. P pac [3] D. L hol [4] K.E Res [5] A. O pre [6] R. D Pro [7] G.Z Beij [8] X. Y colu s in configuration. In this gas inlet device, the gas was d phase, and the liquid was the continuous phase, and itation andmixwere resultedwhen the gas entered the gh this gas inlet device. The possibility of clogging and greatly reduced. Due to the formation of a lot of bub- –liquid contact area andcontact time increased. Thegas , agitation, and elimination of droplets were combined e process, which made the tower simple in structure. ess maintenance was needed [15,17]. r, when a pierced cylindrical gas inlet device was used sized tower, the incoming gas streams began to be 0,21]. In a jet bubble reactor equippedwith this pierced gas inlet device, the gas streams were also distributed 2, 1997, p [9] P. Suess, A tution of C [10] C. Dodev, Bulg. Che [11] C. Dodev, honeycom [12] X. Zhao, H Patent, ZL [13] X. Zhao, H Patent, ZL [14] A. Higler, tion colum 3988–399 [15] S. Guet, G from low 26 (2002) e not all of the reactor space was utilized effectively, er rates of the entire tower decreased. Therefore, it is ply this gas inlet device in middle- or small-sized tow- lfurization and dust removal from waste gas streams at ions ubble reactor with the pierced cylindrical gas inlet n remove SO2 fromwaste gas streams effectively.When ressure drop for the tower is 3 kPa, pH of lime slurry om 5 to 7, the desulfurization efficiency of the tower eed 90%. iquid, and solid phases in the tower contact sufficiently s evenly, and average dust removal efficiency reaches sure drop for this pierced cylindrical gas inlet device is ly low, so is theenergyconsumption forgaspurification. -scale investigation shows that the pierced cylindrical devices for jet bubble reactors have advantages over inlet devices. The pierced cylindrical gas inlet device r in structure, is easier to install, and need less mainte- gements ject was supported by the National Natural Science of China (50778066), the Program for New Century lents in University from the Ministry of Education of T-05-0701), and the Scientific Research Foundation for verseas Chinese Scholars from theMinistry of Education dwasgrantedfinancial support fromChinaPostdoctoral ndation (2005037206). J. Sohlo, Liquid and gas flow patterns in randompackings, Chem. Eng. 6) 95–105. , K. Semkov, C. Dodev, Mathematical modeling of gas distribution in lumns, Chem. Eng. Process. 42 (2003) 931–937. Macchi, J.R. Grace, N. Epstein, Fluid maldistribution effects on phase n three-phase fluidized beds, Chem. Eng. Sci. 56 (2001) 6031–6038. r, Q.H. Ali, Gas distribution in shallow packed beds, Ind. Eng. Chem. 993) 2408–2417. A.M. Ali, P.J. Jansens, Effect of the initial gas maldistribution on the drop of structured packings, Chem. Eng. 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Pierced cylindrical gas inlet device for sulfur dioxide removal from waste gas streams Introduction Materials and methods Design of tower Preparation of waste gas streams and absorbent slurries Procedures for startup and operation of system Measurement of reactor performances Results and discussion Effects of hole-size and gas flow rate on pressure drop Effect of pH value of absorbent on SO2 removal Performances of dust removal Comparison with typical gas inlet device for a jet bubble reactor Comparison of relationships between gas flow rate and pressure drop under various operating conditions for two towers Comparison of relationships between gas flow rate and height of jet bubbling zone Comparison of relationships between pH value and desulfurization efficiency Advantages and disadvantages Conclusions Acknowledgements References