Colunas Para Teste de Carbon Granular NORIT

7/27/2019 Colunas Para Teste de Carbon Granular NORIT

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GRANULARACTIVATED

CARBONEVALUATION


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Introduction.

NORIT Americas Inc. produces over 150 different varieties

of activated carbon. This diverse product line provides many

options for carbon adsorption. Pilot Column testing can aid

in the process of choosing the best carbon for your purifica-

tion needs.


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In liquid phas e a pplica tions, a ctivated ca rbon is used

to remove impurities from potable water, waste-

water, fine chemicals, foods, and pharmaceuticals.

This tec hnica l pa per add ress es how to evalua te

granular activated carbons (GAC) for liquid phase

applications.

The first eva lua tion ste p is to run simple isotherms

(se en below) to dete rmine fea sibility. P ow de red

ca rbon isotherms c an b e used to determine if the

trea tment go a l ca n be met. The proc edure for run-

ning isotherms is available by requesting brochure

number NA 00-3 from NORITAmericas Inc.

Isotherm testing consists of dosing a measured

quantity of powdered carbon into the target solution.Impurities ad so rb o nto the ca rbons s urfac e a nd

are allow ed to rea ch e q uilibrium. While this tes t

provides an indication of how well an impurity may

be removed using activated carbon, it cannot give

definitive s ca le-up da ta for a g ra nula r ca rbon o per-

ation due to a couple of factors:

In a granula r column, dyna mic a ds orption oc curs

because the impurity concentration changes as the

mas s trans fer zone moves through the bed . This

cond ition d oes not exist in a n isotherm test proc e-

dure. Reg eneration effects on multiple cycles ca n-

not be studied s ince the iso therm tes t procedure

uses powdered carbon (only) in a once-through

adsorption process.

Bec aus e of these factors, pilot c olumn tests s hould

be made using the most promising carbons as

indica ted b y the iso therms. This w ill give a mo re

accurate comparison of the carbons, and provide

some scale-up information useful for commercial

system designs.

This text d es cribe s the proce dure for running a

G AC pilot c olumn test a nd eva luating the d a ta.

Data ma nipula tion tec hniq ues a re provided which

allow conversion from test conditions to widely

differing flow rates, effluent concentrations, and

influent co ncentra tion levels. This proced ure ha s

been s ucce ss fully used numerous times to de sign

full scale systems and estimate operating costs.

Isotherm series


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GAC Pilot Columns.

A pilot column test system should include at least four

columns operating in series in order to determine the rate of

movement and size of the mass transfer zone through the

carbon bed, (see Figure 1). Pilot column systems can be pur-

chased or leased from NORIT Americas Inc. or assembled

using basic components. They can be constructed from

glass, plastic, reinforced fiberglass, or metal pipe as dictated

by the corrosiveness of the process fluid. The columns should

be designed to allow loading GAC from the top.

Figure 1

PILOT COLUMN SYSTEM


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P ilot c olumns a re typica lly ope rated dow nflow.

This is usua lly do ne to s imula te a proposed c om-

mercial de sign. A do wnflow d es ign allow s la rge

G AC vess els to be gra vity fed. It also ensures tha t

the carbon bed remains packed and stable during

the service cycle, resulting in maximum contactbetween the carbon and the feed stream. However,

ca re s hould be ta ken to e nsure the c olumns remain

filled with liquid at all times and are not allowed to

dra in during ope ration. This is often acc omplishe d

by fitting the la st co lumn with a ba ck pressure valve.

In some situations an upflow design is preferable.

One advantage is where suspended solids in the

feed create high press ure drop. It is s ugges ted

that s uspended so lids be removed from the feedstrea m prior to entering a G AC c olumn. How ever,

if this will not be possible in the commercial design,

then the effect of suspend ed s olids should b e

inc lude d in the pilot run. In upflow ope rat ion,

most o f the suspended solids wo rk their wa y up

through the G AC bed without a significa nt increas e

in press ure d rop.

It is recomme nded that the pilot c olumns be ba ck-

washed prior to the start of any test and when

exc essive press ure drop deve lops . This would

involve the w a ter or column-trea ted proc ess stream

to be pumped through the bo ttom of the c olumn

a t a flow rate sufficient to expand the bed. Enough

freeb oa rd sho uld be left to permit 30-50% be d

expans ion during ba ckwa shing. Figure 2 show s

bed expansion for several sizes of Granular DARCO

products in wa ter. The exact ba ckwa sh flow rate

will depend upon the visc osity of the wa ter and the

mea n particle diameter of the GAC. The expans ion

ca n a lso be d etermined visua lly in a glass column.

The ca rbon bed sho uld b e a t lea st 24 inches (61

cm) deep and 1.5 inches (about 4 cm) in diameter.

A smaller column is not recommended since the

wa ll effect beco mes significa nt. NORITAmerica s

Inc. typica lly us es 4 inch (10 cm) dia meter c olumns

in its pilot studies.

The bed c an be supported by g la ss wo ol, wire mesh

sc reen, or a w edg ewire sc reen. A typica l sc reen

size is 60 mesh (U.S. Standard Series) or a 0.008

slot opening.

Figure 2

BED EXPANSION CURVE FOR GRANULAR

DARCO ACTIVATED CARBONS


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Selecting Carbon Mesh Sizes.

In the design of a full scale column, GAC mesh

size is very importa nt. NORITAmerica s Inc. offers

DARCO and NORIT brand granular a nd extruded

a ctivate d ca rbons in over a d ozen sizes . Initia lly,

finer mesh carbons show more adsorptive capacitythan coarser carbons because of a significantly

fas ter rate of ads orption. How ever, given time to

reach equilibrium, the coarser carbons will have

the sa me total ca pac ity as the finer ca rbons . The

increas ed a ds orption rate of the s ma ller mesh s ize

ca rbons, how ever, is a t the expense of pressure

drop during c olumn opera tion. The press ure drop

for a 12 x 40 mesh ca rbon is tw ice that of a 12 x

20 carbon, while the pressure drop of a 20 x 40

ca rbon is o ver 3 times tha t of the 12 x 20. Thebes t mes h size for any s pecific a pplica tion w ould

depend upon the dimensions of the ca rbon column

(vesse l), the inlet s tream flow rate &visc os ity, and

the sus pended solids conc entra tion of the inlet

strea m. Figure 3 sho ws the pres sure drop curves

for some mes h sizes of G ranula r DARCO.

Loading the Column.

The c a rbon to be used in the c olumn should first

be thoroughly wetted . This is done to remove air

tra pped in the ca rbon pores tha t wo uld otherwise

prevent the feed liquor from contacting the entire

ca rbon surfac e. In sma ll lab oratory columns, the

carbon is typically slurried with water in a container

and a llowed to soa k. So aking should las t at leas t

30 minutes to a n hour to a llow mos t of the trapped

a ir to diffuse out of the sma lles t pores. In la rge

comme rcial vess els, the c arbon is often left to soa k

overnight prior to ba ckwa shing a nd b eing place d in

service.

Once the ca rbon has soa ked, the fines must be

remove d. C a rbon fines a re pres ent in all gra nula r

a ctiva ted ca rbons. They are genera ted not only in

the ma nufa cturing proces s, but a lso through s hip-

ping a nd handling. If not remove d during loa ding,

fines can cause excessive pressure drop across the

ca rbon column and s horten the c olumns service

life. When loa ding sm a ll co lumns, the c a rbon fines

may be removed b y dec anting, ad ding fresh w ater

and allowing the carbon to settle, and decanting

aga in. This should be repea ted until the wa ter is c lea r,

usua lly 3 or 4 times . In la rge c omme rcia l vesse ls,

the carbon fines are removed by backwashing.

Feed Delivery and Flow Rate Control.

The rec omme nded rang e of conta ct flow is 0.1-3.0

be d vo lumes per hour (B V/hr), depe nding upo n the

deg ree of purifica tion de sired, the type a nd c on-

centration of impurity, the nature of the process

liquor, and pressure drop.

G enerally high levels of impurity loa ding o n the

carbon, high inlet impurity concentrations, andhigh visc os ities w ill req uire a low er inlet flow rate.

The c a rbon w ill perform mo re efficiently a t low flow

rates (longer co ntac t times), but a t the expense o f

the amo unt of liq uid tha t ca n be proces sed through

a column in a given time.

A feed pump s uitab le for ac curate a nd c ontinuous

flow is required since flow rate and total volume of

liquor are the most important controllable variables

in deve loping design da ta . B efore proces s liq uor is

delivered to the ca rbon, suspend ed ma tter should

be removed, preferably by the sa me method

planned for the pla nt sys tem.

Figure 3

PRESSURE DROP CURVES FOR

GRANULAR ACTIVATED CARBONS


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Column Operation.

To d evelop reas ona bly good da ta for sca le-up to

full pla nt de sign, it is importa nt to have the p ilot

columns operating as near as possible to the

a nticipa ted plant opera ting cond itions . The mos t

critica l fa ctors, flow ra te a nd feed impurity c oncen-tration, must be constant for the entire test run.

The tempe rature of the full-sca le influent a nd

effluent streams sho uld a lso b e simula ted . This

ma y req uire prehea ting the feed a nd hea t tape &

insulation on the G AC pilot c olumns.

Se veral sa mples o f the feed s trea m should b e ta ken

over the duration of the test to spot any drift in

impurity co nce ntration. Reg ula r sa mples should

be pulled from the botto m of eac h column. Thesamples should be filtered prior to examination if

the acc urac y of the ana lysis could b e a ffected b y

sus pend ed s olids . When the effluent qua lity from

the la st column in the s eries is unacc eptab le, the

test is s topped.

Data Collection.

The d a ta ca n be co mpiled simila r to Figure 4, which

show s the results o f a pilot co lumn study on a n

a ctua l refinery wa ste wa ter. Effluent impurity con-

centrations for all columns a re plotted a ga inst

elapsed time in Figure 5, generating breakthrough

curves. Figure 5 is a plot show ing w hen eac h col-

umn brea kthrough curve exc eed ed the effluent limit

of 30% COD rema ining . The line through the da ta

points in Figure 6 is the B ed Depth S ervice Time

(B DS T) curve. If the flow rate through the G AC is

cons tant throughout the test a nd there a re no

changes in impurity concentration or composition,

then the service time at breakthrough should be a

linear function of carbon bed depth.

Figure 5

BREAKTHROUGH CURVES

FOR REFINERY WASTE

Figure 4COLUMN EXHAUSTION DATA

COLUMN1 COLUMN 2 COLUMN 3 COLUMN 4TIME % COD % COD % COD % CODHRS. REMAINING REMAINING REMAINING REMAINING

25 20 17 13 1250 25 18 14 1175 33 21 16 12

100 45 22 15 13125 62 26 15 11150 67 27 17 13175 76 31 19 12200 80 33 19 13225 85 40 18 14250 88 44 24 16275 91 45 27 18300 96 48 28 20325 98 55 32 24350 97 59 34 24375 100 64 35 27400 99 68 37 26425 100 70 41 29450 100 75 45 31475 97 74 46 34500 100 78 49 34525 100 76 48 35550 98 78 49 37

575 100 76 50 34600 100 79 51 36


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Data Evaluation.

The b ed de pth s ervice time (BDS T) eq ua tion is

ba sed on work by B ohart and Ada ms,1 Klotz,2

a nd Dole and Klotz.3 It ha s the follow ing form:

t = ax + b

where t Service time a t breakthrough, hours .

x Bed depth, feet.

a S lope = (1990No /Co)V, hrs ./ft.

b Ord ina te inte rc ept =

16.018/(KC o) ln(Co /C b 1), hrs.

No Carbon efficiency, lb impurity/ft3 carbon.

Co Feed impurity concentration, ppm.

V Linear flowrate , gpm/ft2.

K Adsorp tion ra te constant , ft3

of liq uidtreated per lb of impurity fed to the

system per hr., required for the adsorp-

tion wave front to move through a

bed depth eq uivalent to the c ritica l

bed d epth.

Cef Impurity concentration in effluent at

breakthrough, ppm.

The s lope (a ) of the be d d epth service time line in

Figure 6 represents the time required to exhaust

one foot of the c a rbon b ed (under the tes t co ndi-

tions use d), w hich c an a lso be d efined a s the time

required for the adsorption wave front to move

through one foot of the ca rbon bed . The rec iproca l

of the slope is the ra te a t which the ca rbon bed is

spent. An estima te of the ra te at w hich ca rbon is

used to continuously produce acceptable product

liquid (or the rate at which the carbon must be

a dd ed o r regenerated ) ca n be ma de b y multiplying

this rec iproc a l va lue of the slope b y the bulk density

of the carbon.

The BDS Teq uation c an a lso be w ritten in terms

of bed d epth a s a funct ion of time. This a llow s

the abscissa intercept to be calculated as follows:

Xo = -b/a

Xo is the abscissa intercept and represents the

critica l bed de pth. This is de fined a s the minimum

bed depth required to produce a satisfactory effluenta t time zero. The ordinate interce pt (b) represe nts

the rate of adsorption, or the time required for the

a ds orption wa ve front to pa ss through one c ritica l

bed d epth.

Breakthrough points must b e s pecified for eac h

BDS Teq uation that is de veloped. Obviously, for a

given bed depth, the s ervice time a nd the s lope of

the B DST curve w ill decreas e a s the effluent qua lity

requirements increase.


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Changing Process Conditions.

A new B DST eq uation must b e developed if the

linear flow ra te through the bed c hange s. P lotting

a new BDSTcurve will not require additional col-

umn tests. Rather, the new BDS Teq uation can be

ob ta ined simply b y m ultiplying the o riginal s lopevalue by the ra tio of the two rates. The new eq uation

for a cha nge in flow rate is d eveloped a s follow s:

t = V1/ V2ax + b

w here V1 Original flow rate.

V2 New flow rate.

Our experience indicates that the results obtained

by this simplified method w ill be in clos e a greementwith results obta ined b y tes ts pe rformed under

a ctua l flow -ra te c onditions (se e Figure 7). It sho uld

a lso be noted that c hang ing flow rates have little

effect on the ordinate intercept (rate of adsorption).

A new BDSTequation must also be developed if

the c onc entration of the impurities in the feed

cha nges . Aga in, a goo d approxima tion ca n be

obtained by calculation instead of running additional

tes ts. The new s lope is found by m ultiplying the

original slope by the ratio of the impurity concen-

tration of bo th feeds . To find the new o rdinate

intercept, multiply the value of the original intercept

by the same concentration ratio and by the natural

log of the impurity co ncentration. The new eq uation

will have the following form:

t = C1/C2 ax + (C1/C2) ln(C2/Cef 1) b

ln(C1/Cef 1)

w here C1 Original influent c onc entration, p pm.

C2 New influent concentration, ppm.

Goo d a greement is obtained b etween ca lculated

and ac tual values.

Figure 6

BED DEPTH SERVICE TIME RELATIONSHIP

Figure 7

EFFECT OF FLOW RATE CHANGE

ON THE BDST CURVE


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Example Problem.

The da ta displayed in Figure 4 wa s p lotte d in Figure

5 to c rea te b reakthrough c urves for the pilot s ystem.

In our example, 30% COD remaining was selected

a s the effluent-limiting c onc entration. Thus, w e ca n

rea d from these curves the breakthrough times a tthe various bed depths:

Bed ServiceColumn Depth, ft. time, hr.

1 3.3 70

2 6.6 160

3 9.9 340

4 13.2 500

These a re plotted in the form of the BDS T eq uation

des cribe d a bo ve. The line through the break-through points generates the eq uation which is

plotted in Figure 6:

t = 44.5x 100

This c a n be a djuste d to reflec t cha nges in operating

co nditions. For exa mple, if the flow rate is d oubled,

the slope of the line is halved and the intercept

rema ins the sa me. The new eq uation bec omes :

t = 22.3x 100

This line, a long w ith a n a ctua l B DS Tline de rived by

physically running the system at twice the flow rate,

is a lso s how n in Figure 7. New eq uations reflec ting

cha nges in influent concentrations c a n also b e

derived by the method o utlined a bove. Examples

of these c hange s a re s hown in Figure 8.


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System Sizing.

For a fixed bed adsorber, the necessary carbon

bed depth for the desired s ervice life ca n be rea d

direc tly off of the BDS T curve (Figure 6) or ca n be

ca lcula ted using the BDST eq uation. This is a ll

that is neces sa ry to d etermine sys tem size unlessca rbon regeneration is us ed.

Activa ted c arbon c a n be reac tivated therma lly or

in some ca ses c hemica lly regenerated . In most

applications, thermal reactivation is used to restore

most of the virgin GAC a ds orptive c apa city.

However, c hemica l regeneration with ca ustic, a cid,

or solvents ma y be much more cos t-effective

depending on the nature of the impurities on the

ca rbon. If a chemical regeneration scheme is tobe implemented, the regeneration solution should

be run counterflow to the direction of the normal

se rvice flow. Reg a rdless of the regenerant flow

direction, some o f the GAC a ds orptive ca pa city is

los t with ea ch regenera tion/rea ctivation cyc le. If

use of regenerated or rea ctivated G AC is a n option,

it is very important to tes t the e ffect in the pilot

columns. Many systems whose des igns are ba sed

on virgin GAC da ta are undersized when ope rated

with reactivated carbon.

For additional assistance with GAC system design,

plea se conta ct NORITAmerica s Inc.

References.1 Boha rt, G. S ., and Ada ms, E. Q.,Journal of

American Chemical Society, 42; 523-544, 1920.2 Klotz , I. M., Chemical Reviews, 39; 241-268, 1946.3 Dole, M., and Klotz, I. M., Industrial and

Engineering Chemistry, 38; 1289-1297, 1946.

Figure 8

BDST RELATIONSHIP FOR DIFFERING

INFLUENT CONCENTRATIONS


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2001 NORIT NA00-4 2000

www.NORIT.com

NORIT Nederland BV

Amers foort, The Nethe rla nds

Telephone : 31334648911

Telefa x: 31334617429

NORIT (U.K.) Ltd.

Glasgow, Scotland

Telephone : 441416418841Telefa x: 441416410742

NORIT (France) S.a.r.l.

Paris, France

Telephone : 33145910808

Telefa x: 33148673603

NORIT Italia S.p.A

Ravenna, Italy

Telephone : 39544451514

Telefa x: 39544451283

NORIT Deutschland G.m.b.H.

Dsseldorf, G ermany

Telephone : 49211906020

Telefa x: 49211161115

N.V. NORIT Belgium S.A.

Brussels, Belgium

Telephone : 3226750645Telefa x: 3226751119

NORIT (Japan) Co. Ltd.

Mina to-Ku, Tokyo, J a pa n

Telephone : 81352952850

Telefa x: 81352952860

NORIT Singapore Pte. Ltd.

S inga pore, S inga pore

Telephone : 657353066

Telefa x: 657353166

NORIT Americas Inc.

3200 West University Avenue

Marsha ll, TX 75670

800-641-9245

Telephone: 903-923-1000

Telefa x: 903-923-1003

e-mail: info@norit-america s.c om

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