톨루엔 제거를 위한 생물필터 공정의 동적 모사 및 그 해석

신민수, 금영섭*, 이현재**, 최호석

충남대학교 공과대학 화학공학과, 영동대학교 화학공학과*, (주) 한탈**

Dynamic Simulation of the Biofiltration on the Removal of Toluene

Min-Su Shin, Young-Sup Kum*, Hyun-Jae Lee**, Ho-Suk Choi

Department of Chemical Engineering, Chungnam National University

Taejon, 305-764, Korea

Department of Chemical Engineering, Young-Dong Univeristy*

Hantal Co., Ltd.**

Introduction

Biofiltration is an air pollution control technology in which microorganisms immobilized on organic/inorganic packing materials at an off-gas containing biodegradable volatile organic or inorganic compounds and is often a highly efficiency and low-cost alternative to other, more conventional, air pollution control technologies such as thermal oxidation, catalytic incineration, refrigerated condensation, carbon adsorption by chemicals and water scrubbers. Recently, in Europe and Japan, it is the most commonly employed odor control technique. Biofiltration is a very complex process. It involves mass transfer and reaction, and is also affected by the characteristics of the flow of the gas phase through the reactor. Furthermore, the process requires maintenance of proper moisture levels for the biomass to be active; this is usually achieved by humidifying the contaminated material before it enters the reactor. The purpose of this study was to describe on the dynamic simulation of the biofiltration on the removal of toluene. Thus, in this study through the dynamic simulation of the removal of toluene in a known biofilter system, the performance of a biofilter under given conditions and the relationship between parameters such as media surface area, biological activity, biofilm thickness, etc and toluene removal are investigated.

Model Development for Biofilter process

A general model for the biofilter process contains three phases such as gas phase, biofilm phase and solid phase[1,2]. Two mass balances in the biofilm are

[eqn: { PARTIAL s SUB j } over { partial t }~=~f(X sub v ) D sub jw { PARTIAL sup 2 s SUB j } over { partial x sup 2 }~-~ X SUB v over Y sub j mu sub j (s sub j , s sub o )]                                (1)

[eqn: { PARTIAL s SUB o } over { partial t }~=~f(X sub v ) D sub ow { PARTIAL sup 2 s SUB o } over { partial x sup 2 }~-~ X SUB v over Y sub oj mu sub j (s sub j , s sub o )]                                (2)

with initial and boundary conditions

[eqn: t = 0, ~h = 0,~x=0:~ s sub j = {c sub ji,o } over m sub j ~~ s sub o = { c sub oi,o } over m sub o]                                     (3)

[eqn: t = 0, ~0〈h≤H,~x=0:~ s sub j = {c sub j,o (h) } over m sub j ~~ s sub o = { c sub o,o } over m sub o]                               (4)

[eqn: t = 0, ~0〈x≤□:~ s sub j = {s sub j,o(h) } ~~ s sub o = { s sub o,o (x) }]                                     (5)

[eqn: 0〈t〈□, ~h〉u sub g t~x=0:~ s sub j = {c sub j,o (h) } over m sub j ~~ s sub o = { c sub o,o(h) } over m sub o]                          (6a)

[eqn: 0〈t〈□, ~0〈h〈u sub g t~x=0:~ s sub j = {c sub j (h) } over m sub j ~~ s sub o = { c sub o (h) } over m sub o]                        (6b)

[eqn: t〉□, ~h〉0~x=0:~ s sub j = {c sub j (h) } over m sub j ~~ s sub o = { c sub o (h) } over m sub o]                                (6c)

[eqn: t〉□, ~h〉0~x=□:~ {partial s sub j } over partial sub x ~=~0 ~~{partial s sub 0} over partial sub x ~=~0]                              (7)

Mass balances in the gas phase are :

[eqn: □ {partial c sub j } over {partial t }~=~-u sub g { partial c sub j } over { partial h } ~+~D SUB jw f (X sub v ) alpha A SUB s sup * ({partial s sub i } over {partial x }) sub x=0 ~-~k sub a (1-alpha )A sub s sup * ( c sub j - c sub j sup * )]	(8)

[eqn: □ {partial c sub 0 } over {partial t }~=~-u sub g { partial c sub 0 } over { partial h } ~+~D SUB ow f (X sub v ) alpha A SUB s sup * ({partial s sub o } over {partial x }) sub x=0]	(9)

with initial and boundary conditions

[eqn: t = 0 ,~h = 0~~~~~c sub j = c sub ji,0 ~~~c sub o = c sub oi,o]                                        (10)

[eqn: t = 0 ~~ 0〈h≤H ~ c SUB j = c sub j,o (h) ~~c sub o = c sub o,o (h)]                                   (11)

[eqn: t 〉0 ,~h = 0~~~~~c sub j = c sub ji ~~~c sub o = c sub oi]                                          (12)

Mass balance in the solid phase (particles) is

[eqn: (1-□)□ sub p { partial c sub jp } over { partial t } ~=~k sub a (1- alpha)A sub s sup * (c sub j - c sub j sup * )]                                 (13)

with initial condition

[eqn: t = 0,~ h≥ 0 ,~ c sub jp = c sub jp,o (h)]                                                 (14)

The biodegradation kinetics for toluene is

[eqn: mu sub j ( s sub j , sub o ) ={ {mu sub j sup * s sub j } over { K sub j + s sub j + {s sub j sup 2 } over {K sub Ij }}} { { s sub o } over {K sub oj + s sub o } }]                                    (15)

The following Freundlich adsorption isotherm is used to predict the amount of adsorption.

[eqn: c sub jp ~=~k sub d ( c sub j sup * ) sup n]                                                         (16)

Two effectiveness factors are defined as:

[eqn: e sub j = { f (X SUB v ) D SUB jw ( {partial s sub j }over{ partial x} ) sub x=0 } over { delta ( {X SUB v }over { Y sub oj } ) [ mu sub j ( s sub j, s sub o )] sub x=0 }]                                              (17)

[eqn: e sub o = { f (X SUB v ) D SUB ow ( {partial s sub o }over{ partial x} ) sub x=0 } over { delta ( {X SUB v }over { Y sub oj } ) [ mu sub j ( s sub j, s sub o )] sub x=0 }]                                              (18)

Results and discussion

The process was modeled with general mass balance equation which take into account reaction, mass transfer, and adsorption of the pollutant onto the packing material. In the model system, the height of the biofilter bed of the equipment used for the experiment was 68.6cm, and volume of the biofilter bed was 5.15 ×10-3m3. The packing material consisted of a mixture of peat and perlite (2: 3 volume ratio before mixing). The space time is □=7.7min and the inlet toluene concentration is 1.65g/m3. Fig. 1 shows the result of the dynamic simulation under these operating conditions. As shown in Fig. 1, the retention time of pollutants is about 2∼3min. But we could know that it took long time to be steady-state as a result of careful observation of simulation results. This is because the adsorption of toluene is still active while the convection transport and the decomposition of toluene reaches steady-state, as shown in Fig. 2.

Conclusion

Biofilter process was successfully modeled for transient operations. The simulation results agreed very well with the experimental results[1]. Thus, the simulation can be used for predicting a response for the unusual input of toluene in the biofilter. Due to slow adsorption process the whole process did not reach an equilibrium with in a short period.

Fig. 1 Removal of toluene at □=7.7min and CTi =1.65g/□

Fig. 2 Amount of toluene adsorbed at □=7.7min and CTi =1.65g/□

References

1. Zarook, S. M. and Baltzis, B. C., Chem. Eng. Sci., 49, 4347, (1994)

2. Zarook, S. M. and Shaikh, A. A., and Ansar, Z., Chem. Eng. Sci., 52, 759,    (1997)