chapter 4 - waste treatment

8/18/2019 Chapter 4 - Waste Treatment

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Waste Treatment 4 -1

CHAPTER IV

WASTE TREATMENT

4.1 Introduction

Waste is general problem in a chemical plant and is global problem in a

developing country. The waste whether is in solid, liquid, gases or mixture form must

not exceed levels at which they will harm the environment. Normally, a plant takes the

raw materials to produce, through stages of processing steps, one or more products for

sale with purpose to generate income. It is impossible to convert !!" of the raw

materials into saleable products, and there is always some waste or residual. This

follows the second thermodynamics law, which states that, there is no process which can

achieve !!" efficiency. Therefore, waste treatment plays the role to protect the

environment from the wastes from the industries.

Waste treatment is an essential process in order to decrease and minimi#e the

environment pollution, especially for those contain toxic components. It is responsibility

to treat the waste to an acceptable form or level before discharge, as direct discharge of

the unwanted material into the ecosystem will bring about detrimental effects. Waste

treatment is an economic burden to a process plant since it does not bring any economic

advantage to the company participated. $owever, the implication of waste treatment

Production of 100,000 MTA Hydrogen


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plant becomes important with regards to environmental pollution. Thus, waste treatment

is important in order to contribute to a safe environment.

%s far as the environment pollution is concerned, the chemical waste either in the

form of solid, liquid or gases must be treated before being discharge to sewage, drain or

atmosphere. The quality of discharge should comply with &The 'nvironment (uality

)*ewage and Industrial 'ffluents+ egulations -- and 'nvironmental (uality )/lean

%ir+ egulation -01. 2nder these regulations, the factory owner or waste generator

must ensure the waste generated is handle and disposal off appropriately to prevent

environmental pollution. 3isposal of ha#ardous waste on4site or governed by

3epartment of 'nvironment, 5alaysia )36'+ regulations on scheduled waste. The

(uality of discharge should comply with the &'nvironmental (uality )*cheduled

Wastes+ egulations -0-. The requirements are7

a+ 2nder the regulations, ! categories of wastes have been classified as scheduled

wastes.

b+ *cheduled wastes can be stored, recovered and treated within the premises of a

waste generator.

c+ Waste generators shall also keep an up4to4date inventory of scheduled wastes

generated, treated and disposed off.

d+ In the case of transporting the waste from the waste generator to the treatment

and disposal facilities, shall be monitored until it reaches the approved

destination.

The details of the regualtions and standards which concerned with the production of

hydrogen plant is enclosed in %ppendix '.



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4.2 Waste Management Hierarc!

"igure 4.1# Hierarc! o$ Waste Management %&a'is( 1))*+

In the waste management hierarchy, pollution prevention or source reduction is

always the top priority option in waste management decisions. *ource reduction is

defined as any onsite activity, which reduces the volume or ha#ard of waste generated at

a facility. 5eanwhile, recycling is defined as practices in which wastes are either

reclaimed or reused. % reclaimed waste is one, which is processed or treated through

some means to purify it for subsequent reuse, or to recover specific constituents for

reuse. eused waste is those, which serve directly as feedstocks without any treatment.

*ource reduction is most preferred because recycling the generation of waste still occurs

and the recycling process results in waste residues. If these two preferred options were

impossible, then the waste treatment should be considered before the final and least

preferable option disposal is considered.

4.2.1 Waste Management

Waste treatment management should follow some of the steps as below7



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i. "aci,ities P,anning

8acilities plan are documents established to analy#e the technical economic,

environmental and financial factor necessary to select a cost effective waste

management plan. The scope of the facilities plan includes7

a. 9roblems defining

b. Identifying design year needed )usually :! years+.

c. 3efining, developing and analy#ing alternative treatment and disposal systems.

d. *electing a plan

e. 6utlining an implementation plan including arrangements and a schedule for

design and construction

ii. &esign

There are many steps of designing need to be adhered in order to design an

optimum waste treatment plant. /onceptual design is used to finali#e the preliminary

design criteria. $ere, principal engineering decisions are made, equipment is selected

and the layout of the plan. It is also advisable to have topographic surveys.

In preliminary design, the site plan is finali#ed, equipments are defined,

alternative mechanical equipment and piping arrangement are made as well as support

systems and utility requirements are determined. %t this stage, a preliminary cost

estimate can be made and be absorbed into pro;ect budget.

iii. S-ecia, Studies

$ere, the pilot plant testing of equipments or processes are made. It is important

that these investigations be completed before the final design starts in order to eliminate

uncertainties and costly redesign.



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i'. "ina, &esign

$ere construction plans and specification is prepared.


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+ 9roviding, operating and maintaining a treatment plant that consistently meets its

performance requirements.

:+ 5anaging operations and maintenance costs within the required performance

level

=+ 5aintaining equipment to ensure proper operation and service

>+ Training operating personnel

6ne of the principal tools used for plant startup, operation and maintenance is the

operations and maintenance manual. The purpose of this manual is to provide treatment

system personnel with the proper understanding of recommended operating techniques

and procedures, and the references necessary to efficiently operate and maintain their

facilities ?@urton and Tchobanoglous, --A

4./ Waste Minimi0ation and Po,,ution Pre'ention

@ased on all waste management techniques, waste minimi#ation is at our top

priority option in effluent solution to the prevention of future ha#ardous waste problems.

@y using materials more efficiently, industry can the generation of the waste and achieve

the desirable protection of human health and the environment. %t the same time, the

costs of waste management and regulatory compliance can be lowered and long4term

liabilities and risks can be minimi#ed.

$owever, the regulatory requirements and the costs of complying with them that

make it difficult for industry to give waste minimi#ation the priority and resources it

deserves if it is to have broad implementation. In practice, waste minimi#ation is

sometimes subordinated to pollution control, even though reducing waste can be the

most effective way to prevent environmental risk. 9ollution control has dominated over

waste reduction for a long period of time and is only being reserved.



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Waste Treatment 4 -

There are some general approaches to pollution prevention and waste

minimi#ation from stream such as7

i+ Improving process technology and equipment that alter the primary sources

of waste generation.

ii+ Improving plant operations, such as housekeeping, material handling and

equipment maintenance and monitoring and waste trackingB automating

process equipment and integrating mass balance calculations into process

design.

iii+ ecycling a potential waste or portion of it on the site where it is generated.

iv+ *ubstituting raw materials that introduce fewer ha#ardous substances or

smaller quantities of such substances into production process.

v+ edesigning or reformulating the end products.

ecycling is usually the step before pollution control, which may make it the

easiest to recogni#e and implement. $owever, there are important economic limits to

recycling and often other waste reduction opportunities offer greater benefits.

In spite of concerns about product quality, improvements in process technology

and equipment appear to be a viable means of waste minimi#ation. *uch improvements

are important because often an entire waste stream can be eliminated. This method

depends on the type of industry. 5ature industries that use continuous process are likely

to have fewer opportunities for changes in the process technology but they may still

have waste minimi#ation opportunitie.



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Waste Treatment 4 -!

4.4 Waste Treatment $or H!drogen P,ant

4.4.1 Waste Streams $or H!drogen P,ant

Cenerally there are D waste streams from the $ydrogen 9roduction 9lant which

are stream D, :>, =>, = and >:. These waste streams are from five different sources as

shown in 8igure >.:.

*tream = *tream D

*tream :: *tream :>

*tream =: *tream =>

*tream =D *tream =

*tream >! *tream >:

"igure 4.2# Wasteater Source $or H!drogen P,ant

8igure >.: shows the sources of waste of every waste stream of the hydrogen

plant where the streams can be classified into two forms which are liquid stream and

vapor stream. The liquid streams are stream D and stream :>. These streams are


8lash, 84= Eiquid Waste

8lash, 84- Waste water

8lash, 84:


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Waste Treatment 4 -"

discharged from flash, 84= and from flash, 84-. The liquid streams discharged contain

various types of chemical compound including methane, ethane, propane, isobutane, n4

butane, isopentane, n4pentane, n4haxene, hydrogen, carbon monoxide, carbon dioxide,

nitrogen, and water. These chemical compounds must be treated and ensured to comply

with the 5alaysia 'nvironmental (uality %ct -- before discharged into environment.

The vapor streams are stream =>, stream = and stream >:. These streams are from flash,

84:, flash, 84:- and membrane separator, *4=:. These vapor form of waste streams do

contained various types of hydrocarbon and chemical compounds which are mentioned

;ust now in the liquid waste streams.

8or the waste treatment in this $ydrogen 9roduction 9lant, the liquid form waste

streams will be treated separately with the vapor form waste streams. The waste

treatment method for these two different types of streams will be discussed in section

>.>.= and >.>.>. The waste streams composition will be further described in next section.

4.4.2 Waste Streams Com-osition

The composition for every waste streams of the $ydrogen 9roduction 9lant are

shown in Table >. below.

The wastes from this $ydrogen plant have contained various types of chemical

compounds. These all4chemical compounds should be to ensure to comply with the

5alaysia 'nvironmental (uality %ct -> before the waste discharged to the

environment. Therefore, some consideration must be done including7

. To consider from the economic aspect, either the waste can be recover and sell as

product or not

:. To consider the waste properties aspect, either it can be discharged directly ti the

environment or need to treat it before discharged to environment.



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=. To consider from the safety reason, either it is dangerous to the environment

or not.

Ta,e 4.1# Waste Streams Com-osition

Com-onentStream 3 Stream 24 Stream /4

gmo,5r 6 gmo,5r 6 7gmo,5r 6

5ethane !>.=FF= >!.!=00 F.!DDF =.>!F= =:.== .!:F

'thane D.D-! :0.---D :.--0'4!= .D0D'4!D >.0FFD'4!= .D:0'4!>

9ropane ==.-D! =.!=> :.::F'4!F .!!'4!0 D.!!-0'4! .D:0'4!0

Iso4@utane -.::D! =.D=- .>-!'4!- :.D=::'4: .=>!:'4 :.=!>>'4:

N4@utane !.DD! >.!D! .=FFF'4! .D>D:'4= =.F!!'4: .D::'4=

Iso49entane >.:D! .F>! =.0F:='4> .>->='4 .0>=:'4F D.0FD'40

N49entane :.-:D! .:: =.:!D>'4D 0.0D'4- 0.-D-!'40 :.0:F'4-

$exane F.!D! :.==!F 0.0:='4: F.:>0>'4:D :.>00D'4:> .0:D'4:F/arbon

dioxide=.:D! D.!-:0 F!.DD0 .-0F :!.D-:F =-.00-:

Nitrogen !.=0!> !.>D- .FD=D'4! .=FD'4!: 0.0F-D'4! :.0>D'4!:

/arbon

5onoxide!.!!!! !.!!!! .:FFF =.:!:'4! F.FD-> :.!-!'4!

$ydrogen !.!!!! !.!!!! =>.>0:F 0.=>- FF!.:>00 :!.:0!

Water !.!!!! !.!!!! F.D-- .=::>'4!= .DF='4!= >.F!:'4!D

5ethanol !.!!!! !.!!!! !.!!!! !.!!!! :>.= =0.0

Ta,e 4.1 %continued+

Com-onentStream /8 Stream 42

7gmo,5r 6 7gmo,5r 6

5ethane F.D=:'4! .!FF'4! :D:.!00! D!.->=F

'thane .!='4!= .FFF:'4!> :.=!FD'4! >.FF:'4!0

9ropane :.F=>'4! >.:D>>'4!0 .:!D'4 .>DF:'4

Iso4@utane D.!>'4 -.:::0'4: .D0-F'4:> =.::D'4:D



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N4@utane =.!!=='4: >.0D!F'4= :.D-:'4: D.DF'4:0

Iso49entane .D0=:'4F :.DD!'4 :.DDF!'4=D D.FD>'4=F

N49entane .=0>:'40 .-:F'40 .F0'4=0 .DD::'4=0

$exane .:!F'4:> :.-!'4:D =.DF>:'4>- .:!:-'4D!

/arbon dioxide :D.>- >.!>= 0:.:>0> =F.0=!!

Nitrogen :.:D-F'4!: =.F>-D'4!= D.:F=> .!F=/arbon 5onoxide :.F:D'4! >.:>=F'4!: :>.:=> >.0D!

$ydrogen .=:F- :.-0D :=.DD=F >.D--

Water D.:DD'4!> 0.D:!D'4!D -.>D-'4=0 .-!'4=0

5ethanol DD.>:D -:.->> .DF!D .D:-

4.4./ Wasteater Treatment

There are two wastewater streams, *tream D and *tream :> in $ydrogen

9roduction 9lant. These two streams will be flowed in a mixer and a stream consist of

two phase will occured due to the combination of two different conditions of the

streams. The separation process need to be done with the stream before treatment using

flash. The vapor stream is flowed to the vapor stream waste treatment plant for treatment

while the liquid stream will be treated in the wastewater treatment plant.

4.4./.1 Wasteater Treatment P,ant

Introduction o$ Acti'ated S,udge

The activated sludge process is a biological wastewater treatment tehnique in

which a mixture of wastewater and biological sludge )microorganisms+ is agitated and

aerated. The biological solids are subsequently separated from the treated wastewater

and returned to the aeration process as needed.



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The activated sludge process derieves its name from the biological mass formed

when air is continuously in;ected into the wastewater. In this process, microorganisms

are mixed thoroughly with organics under conditions that simulate their growth through

use of the organics as food. %s the microorganisms grow and are mixed by agitation of

the air, the individual organisms clump together )flocculate+ to form an active mass of

microbes )biological floc+ called activated sludge.

Process &escri-tion o$ Wasteater Treatment P,ant

"igure 4./# Process ",o seet o$ Wasteater Treatment P,ant

The process involved in wastewater treatment plant is biological treatment with

activated sludge system. *tream D and *tream :> is fed into a mixer and came out with

*tream W which consist of two phase7 vapor and liquid. *tream W is then fed into a

flash to separate the two phase.


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6rganic waste H 6: /6: H $:6

The biological treatment of wastewater stream is based on the ability of a mixed

population of microorganisms to utili#e organic contaminants as nutrients. 6rganic

constituents can be removed by aerobically converting them into carbon dioxide and

water )minerali#ation+ or by other mean we can anaerobically decompose them into

methane and carbon dioxide or bio transferring to less toxic or non4toxic organic

compounds.

The microorganism population in the biological treatment process can either be

natural or developed to act on specific compounds in the waste. @oth #rocaryotic and

eucaryotic organisms have potential for biological treatment of toxic organic.

'ucaryotic, which includes proto#oa, fungi and most groups of algae, has highly

organi#ed cell structure. 9rocaryotic, which includes bacteria and blue4green algae, has a

much simpler cell structure without a classical nucleus.

@ecause biological systems contain living organism, they require specific ratios

of carbon and nutrients. The most important nutrients are nitrogen, phosphorus andothers. Water is also a necessary component of all living organisms and therefore is a

vital part of the biological waste treatment systems. Industrial wastewater often lacks the

essential macro4 and micronutrients, which must therefore be added during treatment.

The outlet stream from aeration tank is then being pump into a clarifier. $ere, the

microorganisms and suspended particles are given enough time to settle down. The

sludge formed will then be recycled back into the aeration tank. The purpose of

recycling the sludge is to maintain the concentration of microorganisms inside the

aeration tank. The effluent from clarifier will be nearly pure water and is safe to

discharge into drainage system.



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Table >.: shows the summary of the composition of the waste water streams. The

composition of the streams after the flash is calculated in mass balance in %ppendix '.

Ta,e 4.2# Com-osition asteater $or streams

Com-onent

Stream 3%7mo,5r+

Stream 24%7mo,5r+

Stream W1%7mo,5r+

Stream V1%7mo,5r+

Stream 9%7mo,5r+

5ethane !>.=FF= F.!DDF !.>:- !.=:: !.!>-F

'thane D.D-! :.--0'4!= D.D->! D.!!>D !.D0->

9ropane ==.-D! :.::F'4!F ==.-D! =:.--F .!DD>

Iso4@utane -.::D! .>-!'4!- -.::D! 0.>-! !.=>!

N4@utane !.DD! .=FFF'4! !.DD! -.>=: .F0

Iso49entane >.:D! =.0F:='4> >.:D! =.::- .!>D-

N49entane :.-:D! =.:!D>'4D :.-:D! :.!>: !.00=0

$exane F.!D! 0.0:='4: F.!D! :.>-0 =.D-D:/arbon dioxide =.:D! F!.DD0 =.0== =.F=> !.--F

Nitrogen !.=0!> .FD=D'4! !.D>D0 !.D>D> !.!!!=

/arbon 5onoxide !.!!!! .:FFF .:FFF .:FDD !.!!

$ydrogen !.!!!! =>.>0:F =>.>0:F =>.>F: !.!FF>

Water !.!!!! F.D-- F.D-- .FD:! D0.0F-

5ethanol !.!!!! !.!!!! !.!!!! !.!!!! !.!!!!

4.4./.2 Si0ing and Costing o$ Water aste Treatment E:ui-ment

The activated sludge system is used as waste water treatment plant in this

hydrogen plant. The si#ing of this activated sludge system is done based on the

$%ntroduction to &n'ironmenta( &ngineering) 3rd &dition *y +a'is and orne(( from

page =0: to =-.

8rom the literature ?3avis and /ornwell, --0A, the variables are summari#ed as

follows7

( waste water flow rate into aeration tank, mJKday

:.-0- m=Khr x :>hrKday

.>-=F mJKday

G ! microorganism concentration )volatile suspended solids or


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* :! mgKE

* +)

+)

−−

+

d mc

cd .

/

/ /

µ θ

θ

:! +!F.!D)+!F.!)PF!

−−

+

c

c

θ θ

cθ !.0> day

If we assume microorganism concentration in aeration tank, G =!!! mgKE and

*o !!!mgKE, the hydraulic detention time7

G +)

++))

cd

oc

/

. . 0

θ θ

θ

+

−

=!!! +0>.!!F.!)

+:!!!!+)F.!)0>.!

×+

−

θ

θ !.F=0 day

$ydraulic retention time, θ =.-=D hr


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:!!

!F

D!!! mgKE

.!

. =××

< 0.=FDD m=Kday

eturn *ludge flow rate, (r

3 3

3 22 3 223

r

e-r -

−

−−− +)

=!!!D!!!

+:!+)=FDD.0>-=F.)+D!!!+)=FDD.0)+=!!!+)>-=F.)

−

−−−

0D.F-D>mJKday

)/heck this result using 8igure D4:= ?3avis and /ornwell, --0A, showed it is a valid

result.+

iii+ "inding Vo,ume o$ C,ari$ier

8lowrate water from aeration tank to clarifier

(o H (r

< .>-=F H 0D.F-D>

D.0- mJKday

!.!!0 mJKs

2tili#ing an average overflow rate of ==mKday )typical+

*urface area required



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Waste Treatment 4 -1!

daym

daym

K==

K0-.D =

>.F== mR

3iameter of the tank

>.F== mR S3RK>

3 :.>F: m

:.D m

8rom the Table D4: ?3avis and /ornwell, --0A, we select side water depth

)*W3+ of =.>m

Now we must check the solids loading. )mgKEgKmJ+

*E ::

=

=+D.:)

>!!0.!=!!!

m s

m

m

g

×

××

π

day

s

g

5g

sm

g 0F>!!!

F=D!.-

F.:=

: ××

−

-D.!>FF kgKd.mR

8rom 8igure D4: ?3avis and /ornwell, --0A, we find that for an *!!!!0.!

×

×

π

-.0!> mJKd.m

8rom literature ?3avis and /ornwell, --0A, the CE25@ has set

maximum recommended weir loadings for secondary settling tank at :D to :D!

mJKd.m. The WE calculated is below the maximum value, therefore the result is

acceptable.

i'+ Summar! $or Costing Wasteater Treatment E:ui-ment



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Waste Treatment 4 -1"

3etails calculations please refer %ppendix '.

Ta,e 4.4# Summar! $or Costing Wasteater Treatment E:ui-ment

E:ui-ment Cost %RM+ =ti,ities

5ixer 5 :>FD-.!D 5 :0:F.!Kyear 8lash 3rum 5 :::,FD.D- 4

%eration Tank 5 =!,!!!.!! 4

/larifier 5 0!,!!!.!! 4

9ump 5 :, =-.!! 5 =.D0 K year

9ump : 5 =!,=.D 5 =D.!K year

9ump = 5 :F,=D:.=! 5 D>.:>K year

Tank 5 :,00-.0D 4

Total 5 FF=,D-.!- 5 :0,D=0.0>Kyear

4.4././ Rec!c,ed Water Treatment

In the production of hydrogen plant, there is a water recycled which is flowed

from the flash )84+ to the mixer )54+. The main ob;ective of this recycled stream )*4

:+ is to recover the water removed from the process flow and recycle or reuse the water

as raw material for the plant. The water recycled contain contaminates components

)carbon monoxide, methane, hydrogen+ which affect the performance of the ma;or

equipments in the plant such as reactors. The amount of contaminates might be

accumulated from time to time and the purity of the water will become lower and lower.

Therefore in order to prevent the consequences, the recycled water stream must be

treated before flowed into the mixer as raw material. Table >.D shows the composition of

the water recycled stream of the hydrogen plant before treatment.

Ta,e 4.3 Com-osition o$ rec!c,ed stream %S>21+ e$ore treatment

/omponents 8low rate )kgmoleKhr+

5ethane D.F!>D:!>

'thane !.!!D=D>

9ropane .0F=:'4!F

Iso4@utane :.=:=-'4!-

N4@utane :.FD!'4!

Iso49entane .D:0:'4=

N49entane .D=F-F'4>

$exane .!F-'4-

/arbon dioxide :.00==>D-=



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Nitrogen !.D-F00=!D

/arbon 5onoxide .::-=!-

$ydrogen 0F.-D!F=0

Water D-D.!==>=

Total F-!.-0D=D

8rom Table >.D, we can see that the components of the recycled stream are more

or less the same with the waste stream in waste water treatment plant. The only different

is that -F.D" of the composition is consisted of water. Therefore, the same treatment

system activated sludge system is used for the recycled water treatment. In order to

save cost for this production hydrogen plant, the wastewater treatment plant will be used

as the recycled water treatment plant instead of another water treatment plant is built.

The same treatment plant will be used alternately for both wastewater treatment and

recycled water treatment. 8igure >.> shows the layout of water treatment plant.

"igure 4.4# Rec!c,ed Water Treatment S!stem

8rom 8igure >.>, both waste water stream and recycled water stream is treated in

single activated sludge system. @ut the treatment for waste water and recycled water is

carried out alternately where valves are used to control the flow rate of the waste water

stream and recycled water stream. 6nce the


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treatment, the


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treated. 2se of chemicals for phosphorus removal can add another .! percent. The

sludge withdrawn from the treatment processes are still largely water, as much as -

percent ?3avis and /ornwell, --0A.

*ludge treatment processes are concern with the removal of the large amount if

water from the solid residues. In this section, the basic processes for sludge treatment are

introduced and described briefly. The basic processes are7

a+ Thickening7 *eparating as much as water as possible by gravity or flotation.

b+ *tabili#ation7 /onverting the organic solids to more refractory )inert+ forms so

that they can be handled or used as soil conditioners without causing a nuisance

or health ha#ard through processes referred to as &digestion1. )These are

biochemical oxidation processes.+

c+ /onditioning7 Treating the sludge with chemicals or heat so that the water can be

readily separated.

d+ 3ewatering7 *eparating water by sub;ecting the sludge to vacuum, pressure or

drying.

e+ eduction7 /onverting the solids to a stable form by wet oxidation or

incineration. )These are chemical oxidation processesB they decrease the volume

of sludge.+

4.4./.3 S,udge &is-osa,

The wastewater treatment plant )WWT9+ process residuals )leftover sludge+ are

unavoidable in the industrial and have to be proper disposed. There are two ways of

disposing the residuals of WWT9 )either treated or untreated sludge+ which are

considered feasible. These two methods are land disposal and utili#ation of the sludge to

produce a product. %mong these two methods, land disposal is considered as more

practicable. In this section, we will roughly introduce these two types of sludge disposal

methods which might be applied in our hydrogen production plantUs WWT9.



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@asically, the land disposal is divided into three categories7 land spreading,

landfilling and dedicated land disposal. The brief description of these three categories is

explained.

@and S-reading

Eand spreading is the practice of applying WWT9 residuals for the purposes of

recovering nutrients, water or reclaiming despoiled land such as strip mine soils. In

contrast to other land disposal techniques, land spreading is land4use intensive. The

application rates of this method are governed by the character of the soil and the ability

of the crops or forests on which the sludge is spread to accommodate it.

@and$i,,ing

*ludge landfill can be defined as the planned burial of wastewater solids,

including processed sludge, screenings, grit and ash, as a designated site. The solids are

placed into a prepared site or excavated trench and covered with a layer of soil. The soil

cover must be deeper than the depth of the plow #one )about !.:! to !.:D m+. 8or the

most part, landfilling of screenings, grit and ash is accomplished with methods similar to

those used for sludge landfilling.

&edicated @and &is-osa, %&@&+

3edicated land disposal means the application of heavy sludge loadings to some

finite land area that has limited public access and has been set aside or dedicated for all

time to the disposal of the wastewater sludge. 3edicated land disposal does not mean in4

place utili#ation. No crops may be grown. 3edicated sites typically receive liquid

sludge. While application of dewatered sludge is possible but not common. In addition,

disposal of dewatered sludge in landfill is generally more cost4effective.



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4.4.4 Waste as Treatment

In this hydrogen production plant, there are = main vapor waste streams which

are *tream =>, *tream = and *tream >:. With an extra one vapor waste stream from the

separation unit )flash drum+ of the wastewater treatment plant, there are total > vapor

waste streams which are to be treated in the waste gas treatment.

Incineration or combustion is most common ways to treat the gaseous waste. It

is deemed the most appropriate disposal method for these gaseous wastes ?Mroschwit#,

-0DA since the organic compounds in these streams can rapidly oxidi#ed at high

temperature. The latter differs from the former in that is it involves recovery of energy in

the form of heat generated from the process. 3ecision to either operate the unit as an

incinerator or combustor weighs heavily on economic scale, with unprofitable energy

recovery not uncommon due to the high capacity and operating costs of auxiliary

equipment. 8lare or incinerator, from a different view point is used to minimi#e the

emission of toxic and dangerous substances as it is designed to push the reaction as close

as possible to completion, leaving a minimum of unburned compounds ?9eavy et al,

-0DA.

4.4.4.1 Incineration S!stem

Cenerally, there are four basic types of gas incineration system7

i 3irect 8lame Incineration

ii 8lares

iii /atalytic Incineration

iv Thermal Incineration



25/39


&irect ",ame Incineration

In direct flame incineration, waste gases are burned directly in a combustor with

or without the addition of a supplementary fuel. In some cases, heat value and oxygen

content of the waste gases are sufficient to allow them to burn on their own. 5ore often

than not, the introduction of air or the addition of a small amount of fuel will bring the

gaseous mixture to its combustion point.

3irect flame incinerator )8igure >.D+, also refers to as fume incinerators and gas

combustors, are chambers provided with supplemental fuel burners which provide heat

and retention time to destroy gaseous waste materials ?@runner, -0>A. The desired

combustion chamber temperature is maintained by altering the rate of supplementary

fuel entering the furnace as controlled by appropriate control circuit. Its primary use

being for odor control, toxicity elimination or visible emissions, these incinerators are

applicable for most gaseous waste.

$owever this treatment is not suitable for waste stream that contains high

concentration of nitrogen due to forming of nitrogen oxides )N6x+ is inevitable due to

high temperature burning for sufficiently long period of time. Thermal N6x formed at

temperatures well aboveF!!M ?3avis and /ornwell,--0A. The configuration of this

equipment lends itself to heat recovery at which two modes are existent. In one case, a

heat exchanger utili#es the high temperatures in combust exhaust to preheat the

incoming combustion air. The second case, on the other hand, consists of a heat

exchanger heating a stream for external use, which can be gas or water to steam.

In normal operation, incinerator is designed for complete destruction of organic

components by incineration, with particulate matter discharges almost nonexistent.



26/39


Where other components are present in the gas such as sulfur or halogen, scrubber will

usually be required.

"igure 4.3# &irect ",ame Incinerator

",ares

8lares being a low cost means disposal of relatively large amounts of gas

containing combustible components, they are suited to processes, which are not

continuous. /ontinuous gas generation often lends itself towards heat recovery. 8lares

handle process upset and emergency gas releases that the base load system is not

designed to recover. $eat recovery, almost by definition, is not possible with a flare.

Two types of flares are currently in use, namely the ground level and elevated or

tower flares. Cround flares can be used where there is sufficient space around the flare to

provide for safety of personnel and equipment. The tower flare is more preferred choice



27/39


where space is limited as it keeps the flame above the level of surrounding equipment

and personnel, as well as to promote the dilution of its products of combustion into the

air. Temperature developed in flare system normally ranges from !!4=!°/

?@runner,-0>A.

Cata,!tic Incineration

/atalytic incineration is another method available when combustible materials in

the waste gas are too low to make direct4flame incineration feasible. It is normally used

to destroy waste at low concentrations, less than :D " of the lower explosive limits

?@runner,-0>A.


"igure 4.?# T!-ica, Steam>Assisted ",are S!stem


28/39


8actors that affect the performance of a catalytic incinerator includes operating

temperature, space velocity, volatile organic compounds composition and concentration,

catalyst properties and finally the presence of poisons Kinhibitors in the emission stream.

The important variables are the operating temperature and space velocity )defined as the

volumetric flow rate of the combined gas stream+.

% catalytic incinerator generally consists of a preheating section and a catalytic

section. $owever, cold catalytic systems are now available that operates at ambient

temperature, eliminating the need for pre4heater. The combustion catalyst consists of

basic material, such as activated alumina, impregnated with a metallic compound. The

catalyst has the property of increasing the rate of oxidation at lower temperatures that is

the use of catalyst promotes destruction of gaseous waste at lower temperature. /atalysts

that are normally used are palladium and metal oxides. The gas stream must be free of

particulate matter to avoid the fouling of catalyst. Thus, pretreatment of gas in the form

of cyclonic separation or electrostatic precipitation, may be necessary upstream of the

catalyst is needed.

% fan is located after burner housing to mix the gases and to distribute them

evenly over the catalyst. *upplemental fuel usage for catalyst incinerator is generally

lower than for thermal incinerators, thus reducing operating costs.

%s with direct flame incineration, cost of heat exchange equipment is often more

than offset the savings in supplemental fuel consumption. Investment in larger heat

exchangers will obviously increase the rate of heat recovery. 3ue to its high cost of

maintenance and catalytic poisoning, this system is usually not preferred.



29/39


Terma, Incineration

Thermal incinerator is used when the concentration of combustible materials is

too low to make direct4flame. It is widely used as an air pollution control technique

whereby organic vapors are oxidi#ed at high temperatures.

The most important variables to be considered in the design of this system are

the combustion temperature and residence time since they determine the incineratorUs


"igure 4.8# Scematic &iagram o$ Cata,!tic Incinerator S!stem

%=S EPA Handoo7( Se-t. 1)*?+


30/39


destruction efficiency )3'+. Thermal incinerator can achieve a wide range of destruction

efficiency.

The waste is preheated, often by the use of a heat exchanger utili#ing heat

produced by the thermal incinerator itself. The preheated gas is directed into a

combustion #one equipped with a burner supplied with fuel. The temperature of

operation depends upon the nature of the pollutants in the waste gas. % thermal

incinerator requires a strict design for safe and efficient operation.

Thermal incinerator, as complex as its name sounds, requires stringently careful

design for provide safe, efficient operation. The three TUs of combustion )time,

temperature, turbulence+ and oxygen level must be carefully monitored to prevent the

production of 9I/ )products of incomplete combustion+. Ideally, the relatively clean

stream of hot air produced is used as heat source for other operations within the

industrial plant and offers the potential to be further incorporated into the $eat

'xchanger Network )$'N+ for maximum recovery of heat.

"igure 4.*# Scematic &iagram o$ A Terma, Incinerator S!stem.


/ombustion %ir

*upplementary

8uel

Thermal

Incinerator

'mission *ource

3ilution %ir

$eat

'xchanger

*crubber

*tack


31/39


4.4.4.2 Scruer

9acked scrubber generally is arranged in one of the four ways based in which the

liquid is contacted with the gas stream. /oncurrent flow scrubbers make up two of these

classificationsB in both cases the liquid and gas flow in the same direction.

In a hori#ontal concurrent scrubber, the gas velocity carries scrubbing liquid

into the packed bed and the device actually operates as a wetted entrainment separator.

Normally, superficial gas velocity is limited to a maximum of -.F ftKs due to liquid re4

entrainment at higher velocities. 9acked bed thickness is restricted because the

allowable gas velocity limits the depth of liquid penetration into the tower packing.

% vertical concurrent scrubber can operate at very high velocities so that

pressure drops from inch $:6Kft to as high as = inch $:6Kft are common. There is no

flooding limit of the packing because the liquid holdup in the packed bed decreases as

the gas rate increases. /ontact time between gas and liquid is a function of bed depth as

well as the gas velocity. %bsorption driving forces are reduced because the exit gas is in

contact with the highest concentration of contaminant in the liquid phase. The exit gas

phase may contain substantial liquid entrainment that must be removed before this gas

is discharged into the atmosphere.

The third class of scrubber is called cross flow. This device contacts a

hori#ontally flowing gas stream with a vertically descending liquid flow. Thus, cross

sectional area for gas flow is different flow the area for liquid flow. Eiquid flow rates as

low as :.F galKmin per !!! ft=Kmin of gas may be possible with this arrangement rather



32/39


than a minimum liquid rate of >.: galKmin per !!! ft =Kmin when the gas flow area is

the same as the liquid flow area ?Ceankoplis, --=A.

5ass transfer driving forces are intermediate between vertical concurrent

scrubbers and counter current scrubbers. If the absorbed solute obeys $enryUs law in the

liquid phase, the mass transfer driving force will limit solute removal efficiency to

about -! " for typical chemical fumes assuming scrubbing water flow is limited.

$owever, if the absorption of solute is followed by a rapid chemical reaction in the

liquid phase so that there is no appreciable vapor pressure of solute above the solution,

the mass transfer driving force will be the same as for a countercurrent scrubber.

The most widely used type of scrubber operates with gas and liquid in

countercurrent flow as the liquid flows vertically downward under the influence of

gravity. 5aximum gas flow rate is limited by liquid entrainment or by pressure drop.

9acked bed depth as well as gas velocity controls contact time between the gas and the

liquid phases. 5ass transfer driving forces are maximi#ed because the exit gas stream

contacts the entering liquid, which contains a minimum or #ero solute concentration.

The pressure drop through the tower packing is very important because the cost

of power to move the gas stream through the scrubber may be the largest operating cost

factor. 5ost tower packing manufacturers can provide experimental pressure drop data

specific to the airKwater system. /ountercurrent scrubbers generally have these

characteristics ?Ceankoplis, --=A7

i.3esigned to operate at a pressure drop between !.:D inch $:6Kft and !.F! inch

$:6Kft of packed depth.

ii. %ir velocity normally between D.D ftKs and 0.! ftKs if modern, high capacity

plastic tower packing is used.

iii. Inlet concentrations of contaminant in the gas stream normally do not exceed

D!!! ppm by volume.



33/39


iv. Eiquid irrigation rates typically are from : galKminKft: of column cross

sectional area.

Thus, the countercurrent scrubber is chosen to remove the sulfur present in the

gas flow from the incinerator. The decision to choose a countercurrent scrubber is

because of the inlet gas concentration is at -!°/ and !.=:D k9a.

4.4.4./ Cimne!

*everal types of chimney )referred to as stack by some industry+ are used to

discharge incinerator flue gases into the ambient atmosphere. *tub or short chimney are

usually fabricated of steel and extend a minimum distance upward from the discharge ofan induced draft fan. These are constructed either of unlined or refractory4lined steel

plate, or entirely of refractory and structural brick. Tall stacks are constructed of the

same material as short stacks and are used to provide a greater pressure difference

driving force )draft+ than that resulting from the shorter stacks and to obtain more

effective dispersion of the flue gas effluent into the atmosphere.

*ome chemical and utility application use metal stacks that are made of a double

wall with an air space between the metal sheets. This double wall provides an insulating

air pocket to prevent condensation on the inside of the chimney and thus avoid corrosion

of the metal.

%n important factor in handling acid gases in a chimney involves maintaining a

high internal temperature. This often retards the detrimental effect on the masonry

without the necessity for other precautions. If the flue gases are such that high

temperatures alone are not sufficient, it may be necessary to protect the main walls by

using an independent lining for the full height of the stack, and with a =4> inch air space

between the lining and the main walls. The independent lining must be built of

impervious brick with a low content and acid4proof mortarB very thin ;oints should be

used. The mortar should be carefully chosen for its resistance not only to the particular



34/39


acid involved, but to moisture as well. In addition, the top of the chimney should be

protected by a cap covering both the lining and main walls and made of material not

affected by the flue gas. While room should be allowed for expansion, fumes and

moisture must be not allowed to penetrate under the cap.

4.4.4.4 ases Waste Treatment P,ant

The composition of the vapor waste streams which are treated is shown in Table

>.. While 8igure >.0 shows the gases waste treatment plant of the $ydrogen 9roduction

9lant. 8or this gases waste treatment plant, the incinerator will be used to burn all the

components in the waste vapor streams except carbon dioxide and water.

Ta,e 4.8# Com-osition o$ Va-or Waste Streams

Com-onent

Stream /4

%7mo,5r+

Stream /8

%7mo,5r+

Stream 42

%7mo,5r+

Stream V1%7mo,5r+

5ethane =:.== F.D=:'4! :D:.!00! !.=::

'thane >.0FFD'4!= .!='4!= :.=!FD'4! D.!!>D

9ropane D.!!-0'4! :.F=>'4! .:!D'4 =:.--F

Iso4@utane .=>!:'4 D.!>'4 .D0-F'4:> 0.>-!

N4@utane =.F!!'4: =.!!=='4: :.D-:'4: -.>=:

Iso49entane .0>=:'4F .D0=:'4F :.DDF!'4=D =.::-

N49entane 0.-D-!'40 .=0>:'40 .F0'4=0 :.!>:

$exane :.>00D'4:> .:!F'4:> =.DF>:'4>- :.>-0

/arbon dioxide :!.D-:F :D.>- 0:.:>0> =.F=>

Nitrogen 0.0F-D'4! :.:D-F'4!: D.:F=> !.D>D>

/arbon 5onoxide F.FD-> :.F:D'4! :>.:=> .:FDD

$ydrogen FF!.:>00 .=:F- :=.DD=F =>.>F:Water .DF='4!= D.:DD'4!> -.>D-'4=0 .FD:!

5ethanol :>.= DD.>:D .DF!D !.!!!!



35/39


Mixer

Stream V1

Stream 34

Stream 37

Stream 42

Stream V2

Stream V3

Incinerator

To Chimney

Cooling W ater

Steam

Stream V4

Heat

Exchanger

"igure 4.)# ",oseet $ ases Waste Treatment P,ant

Waste treatment system consists of three equipments7 mixer, incinerator and

chimney+ as shown in 8igure >.-. Incinerator is considered as the main equipment where

combustion occur. Caseous waste streams, *tream =>, *tream =, *tream >: and *tream


36/39


pollution to the environment )atmosphere+. The effluent stream )*tream + is flowed

through a chimney before releasing to atmosphere.

4.4.4.3 Mass ;a,ance Ca,cu,ation

The mass balance for each stream waste treatment plant is summari#ed in the

Table >.0 below. The detail calculation can be referred to %ppendix '.

Ta,e 4.*# Summar! $ Mass ;a,ance n Waste Va-or Treatment P,ant

Com-onent Stream V2 Stream V/ Stream V45ethane =-D.0D: !.!!!! !.!!!!

'thane D.!!> !.!!!! !.!!!!

9ropane =:.--F !.!!!! !.!!!!

Iso4@utane 0.>-! !.!!!! !.!!!!

N4@utane -.>=: !.!!!! !.!!!!

Iso49entane =.::- !.!!!! !.!!!!

N49entane :.!>: !.!!!! !.!!!!

$exane :.>-0 !.!!!! !.!!!!

/arbon dioxide FD.00! >:!0.00F= >:!0.00F=

Nitrogen F.0= 0DD.!-! 0DD.!-!

/arbon 5onoxide =:.= !.!!!! !.!!!!$ydrogen 0=D.D>DD !.!!!! !.!!!!

Water .FD>! D=>.D==D D=>.D==D

5ethanol -.:!= !.!!!! !.!!!!

6xygen !.!!!! >D=.!F0 >D=.!F0

Tota, 4*8B.8?1* 2)131.3*4? 2)131.3*4?

4.4.4.? Energ! ;a,ance $or Waste Va-or Treatment P,ant

Ta,e 4.)# Summar! $ Energ! ;a,ance n Waste Va-or Treatment P,ant

E:ui-ment Heat &ut! %5r+

Incinerator .D='H:



37/39


Heat EDcanger =.:!'H

Table >.- shows the heat duty of two ma;or equipments in the waste vapor

treatment plant. 8rom the energy balance, the incinerator heat duty is .D='H:Khr

and the heat exchanger duty is =.:!'HKhr. The detail calculation is shown in

%ppendix '.

4.4.4.8 E:ui-ment Si0ing

The detail calculations for equipment si#ing are shown in the %ppendix '. Thefollowing tables are the summary of each equipment.

1. MiDer

Tem-erature %C+ >-.-D

Pressure %atm+ !.

Vo,ume %m/+ =D0F.>>D!

&iameter %m+ D.F->

2. Cata,!tic Incinerator

Tem-erature %C+ D0!

Pressure %atm+

&iameter %m+ =.=DF

@engt %m+ =.!>0

/. Heat eDcanger

Area %m2+ --:.F>- m:

In,et ater tem-erature %C+ =!

In,et ater -ressure %ar+ 0

ut,et steam tem-erature %C+ :F!

ut,et steam -ressure %ar+ 0



38/39


4. Cimne!

Tem-erature %C+ =!

Pressure %atm+

Heigt %m+ D0.!F=0

&iameter %m+ .:

4.4.4.* E:ui-ment and =ti,it! Costing

The detail calculation of the equipment and utility costing are shown in%ppendix ' respectively. The following tables )Table >.! and Table >.+ show the

summary of the each equipment and utility cost.

Ta,e 4.1B# E:ui-ment Costing "or Waste Treatment P,ant

E:ui-ment Cost

5ixer 5 :,>FD,-!.>0

/atalytic incinerator 5 =,-:0,!=-.D

$eat exchanger 5 D-,0!.-F

/himney 5 F-,=D.:D

Total 5 ,D>,-:F.:D

Ta,e 4.11# Annua, =ti,it! Cost "or Waste Treatment P,ant

=ti,it! Annua, -urcase cost

/ooling water 5 ,=!,0!0.F

'lectricity 5 :0>,=D.



39/39


4.4.4.) Conc,usion o$ ases Waste Treatment

%fter going through the waste gaseous waste treatment plant, the percentage of

reduction of each component in final emission stream is shown in Table >.:. This plant

is very effective as percentages of organic component discharged are reduced

significantly.

Ta,e 4.12# Reduction o$ Waste A$ter Waste Treatment

Com-onents;e$ore treatment

%7mo,5r+

A$ter treatment

%7mo,5r+Reduction %6+

5ethane =-D.0D: !.!!!! !!

'thane D.!!> !.!!!! !!

9ropane =:.--F !.!!!! !!

Iso4@utane 0.>-! !.!!!! !! N4@utane -.>=: !.!!!! !!

Iso49entane =.::- !.!!!! !!

N49entane :.!>: !.!!!! !!

$exane :.>-0 !.!!!! !!

/arbon 5onoxide =:.= !.!!!! !!

$ydrogen 0=D.D>DD !.!!!! !!

5ethanol -.:!= !.!!!! !!

8rom the summary result above, all the organic wastes are completely oxidi#ed

in incinerator. The heat of recovery system in this waste treatment plant generates

,:>-.0D0> kmolKhr steam at T :F!V/ and pressure 0 bar. The detail calculation is

shown in %ppendix '.

chapter 4 - waste treatment

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