Quencher TOWER Design

8/9/2019 Quencher TOWER Design

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DESIGN OF QUENCHER

CHAPTER No.7

DESIGN OF QUENCHER7.1 QUENCHER:-

The word quencher means sudden cooling. It may be used for various purposes, e.g. for

hardening of solid surfaces, for stopping further reactions etc. In our case quenching ofthe reactor product is needed for sudden cooling, for removing impurities and to avoid

side reactions. Cooling by liquid quenching is essentially accomplished by introducing

the hot gases into a liquid contacting device.

When the liquid evaporates the energy necessary to vaporie the liquid is obtained at thee!pense of hot combustion gases, resulting in a reduction of gas temperature. The

temperature of the combustion gases discharge from the quencher is at the adiabaticsaturation temperature of the combustion gases if the operation is adiabatic and the gas

leaves the quencher saturated with water vapors.

7.2 WHY QUENCHING?

Quenching is choosing in contrast to heat echanger !ecause:

". If an e!changer is used large area is required.#. $lso, direct contact is more efficient than indirect contact.

%. The fine particles from the reactor will also be removed which may otherwise

erode e!changer tubes.Quenching is "i##erent #ro$ coo%ing in the sense that:

". Cooling is done in a comparatively longer time.

#. It also does not stop the side reactions completely.

%. While in quencher formation of by&products are completely stopped.

7.& 'Y(E) *+ QUENCHER:

There are three types of quenchers that may be employed.

". 'pray towers

#. (enture scrubbers

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Production of Acrylonitrile


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DESIGN OF QUENCHER

%. )ac*ed towers

7., )EEC'I*N CRI'ERI:

'pray tower is selected from the above mentioned types of quencher as+". 'pray towers can be used for gas absorption, which removes impurities.

#. The main advantage of spray towers over other scrubber is their completely open

design. It is simple to construct. This feature eliminates many of the scale build up

and plugging problems associated with other scrubbers.%. This is an ine!pensive controlled device primarily used for gas conditioning

cooling or humidification-.

. It requires very little space and only that amount of water is used that is needed to

maintain the desired temperature of the gases at the discharge.

/. Their installation and operation cost are generally considered to b less than that for

other cooling method.0. 'pray towers are very effective in removing pollutants particles from reactor- if

the pollutants are highly soluble.

7./ 0EERI') *+ EN'URI )CRU33ER):

". In venture scrubber contact area available for water and gases is less.

#. $ precooler is to be used when venture scrubber is used for removing particulates.

%. There construction is not so simple.

. 1arge amount of water is required for cooling.

7.4 0EERI') *+ (C5E0 '*WER:

". In pac*ed tower pressure drop is higher.

#. )ac*ing material increases the cost of the tower.

%. It is less efficient than cooler.

. )roblems li*e plugging, fouling and channeling are associated with it.

7.7 )(RY '*WER):-

'pray towers or spray chambers consist of empty cylindrical vessels made of steelor

plasticand noles that spray liquid into the vessels. The inlet gas stream usually enters

the bottom of the tower and moves upward, while liquid is sprayed downward from one

or more levels. This flow of inlet gas and liquid in the opposite direction is called

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http://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Plastichttp://en.wikipedia.org/wiki/Plastichttp://en.wikipedia.org/wiki/Steel


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DESIGN OF QUENCHER

countercurrentflow.Countercurrentflow e!poses the outlet gas with the lowestpollutant

concentration to the freshest scrubbing liquid.

2any noles are placed across the tower at

different heights to spray all of the gas as it

moves up through the tower. The reasons forusing many noles is to ma!imie the number

of fine droplets impacting the pollutant particlesand to provide a large surface area for absorbing

gas.

Theoretically, the smaller the droplets formed,

the higher the collection efficiency achieved for

both gaseous and particulatepollutants. 3owever,

the liquid droplets must be large enough to not becarried out of the scrubberby the scrubbed outlet

gas stream. Therefore, spray towers use nolesto produce droplets that are usually /44 to ",444

5m in diameter. $lthough small in sie, these

droplets are large compared to those created in the

venturi scrubbersthat are "4 to /4 5m in sie.

In a spray tower, absorptioncan be increased by

decreasing the sie of the liquid droplets and6or

increasing the liquid&to&gas ratio167-. 3owever, to

accomplish either of these, an increase in both power

consumed and operating cost is required. In addition,

the physical sie of the spray tower will limit the amount of liquid and the sie of dropletsthat can be used. Cooling hot gases with the acidic quench is relatively simple and

required very little space. 8nly that amount of water is used that is needed to maintain the

desire temperature of the gases at the discharge. Their installation and operating costs are

generally considered to be less than that for other cooling methods.

7.6 )(RY N*E:-

$ spray nole is a device that facilitates the formation of spray. When a liquid is

dispersed as a stream of droplets atomiation-, it is called a spray. 'pray noles are used

to achieve two primary functions+ increase liquid surface area to enhance evaporation, ordistribute a liquid over an area. It is a device which ma*es use of the pressure energy of a

liquid to increase its velocity through an orifice and brea*s it into drops. 9ach nole type

has a specific type of characteristics and capabilities and is designed for use under certain

application conditions.

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http://en.wikipedia.org/wiki/Countercurrenthttp://en.wikipedia.org/wiki/Countercurrenthttp://en.wikipedia.org/wiki/Pollutanthttp://en.wikipedia.org/wiki/Absorption_(chemistry)http://en.wikipedia.org/wiki/Pollutanthttp://en.wikipedia.org/wiki/Scrubberhttp://en.wikipedia.org/wiki/Venturi_scrubberhttp://en.wikipedia.org/wiki/Absorption_(chemistry)http://en.wikipedia.org/wiki/Liquid-to-gas_ratiohttp://en.wikipedia.org/wiki/Sprayhttp://en.wikipedia.org/wiki/Atomizationhttp://en.wikipedia.org/wiki/Countercurrenthttp://en.wikipedia.org/wiki/Countercurrenthttp://en.wikipedia.org/wiki/Pollutanthttp://en.wikipedia.org/wiki/Absorption_(chemistry)http://en.wikipedia.org/wiki/Pollutanthttp://en.wikipedia.org/wiki/Scrubberhttp://en.wikipedia.org/wiki/Venturi_scrubberhttp://en.wikipedia.org/wiki/Absorption_(chemistry)http://en.wikipedia.org/wiki/Liquid-to-gas_ratiohttp://en.wikipedia.org/wiki/Sprayhttp://en.wikipedia.org/wiki/Atomization


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DESIGN OF QUENCHER

7.8 'Y(E) *+ )(RY N*E):

'pray noles can be categoried into several types based on the energy input used+

1. H9"rau%ic sra9:

The hydraulic spray nole utilies the liquid *inetic energy as the energy source to brea*

the liquid into droplets. This type of spray is less energy consuming than a gas atomiedor twin&fluid spray nole. $s the fluid pressure increases the flow increases and the drop

sie decreases. :ut this leads to problems in selecting a droplet sie and to achieve a

certain flow rate at a given pressure. To overcome this situation a special hydraulic nole

1echler'pillbac* ;ole- has been developed. This nole can vary the liquid flow rate

at a particular droplet sie and pressure. This nole creates a better and optimum control

on the liquid spray and in certain applications can eliminate the need of e!pensivecompressed air.

2. Gas ;air< ato$i=e" sra9:

$ir, steam or other gases can brea* up a liquid to form a spray, with the gas providing a

source of energy.

I. Interna% $iing

Internal mi!ing noles mi! fluids inside the nole.

The gas atomied spray utilies a gaseous source to brea* the liquid to the droplets. Theinternal mi!ed twin fluid spray can utilie two different ways for spraying liquid+

In the #irst t9e, the liquid impinges upon a surface for impact to brea* the liquid streamand then the air is mi!ed to atomie it. The advantage of this process is to reduce the

amount of air required to generate the droplets but the downside is that the over time the

impact surface becomes eroded and effects the spray droplet sie pattern. The nole life

can be very short if the liquid has impurities in it.

In the secon" t9e, the liquid is bro*en into droplets by using only gas. The advantage of

this type is that the nole lasts longer but the downside is that this type of spray needs

more gas to generate the same sie of droplets.

II. Eterna% $iing

9!ternal mi!ing noles mi! fluids outside the nole.

9!

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DESIGN OF QUENCHER

7.1> 0E)IGN *+ QUENCHER:-

'uperficial (elocity > (s> 4./ m6s

7as density > G @ 0.?#@ *g6 m%

2ass flow rate of gas > W7> ""A?@ *g6hr

rea o# the Quencher:

$rea > W76 %044 (sG

$rea > ""A?@6 %044 ! 4./ ! 0.?#@

$ > ?."@0 m#

0ia$eter o# the Quencher :

$ > B

#

6 ?."@0 > %.""0 ! #6

> %."? m

og ean 'e$erature 0i##erence +

D T 12T> D T"& D T#ln D T"6D T#-

D T 12T> @#."oC

)uer#icia% ass e%ocities:

Eor 7as 'tream, 7 > mass flow

area

7 > 0/#?.#0 *g6m#.hr

Eor 1iquid 'tream, 1 > mass flow

$rea

1 > "?"#

?."@0

1> #4@" *g 6m#.hr

Rate *# Heat 'rans#er:

q > moCpDT

9#



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DESIGN OF QUENCHER

Where

mo> molar flow rate of liquid stream > ?@/.? *mol 6hr

q > heat rate required to vaporie the water to discharge temperature

Cp> A./% F 6*mol .G

DT > @#." oC

q > %44%?#?."%" F6hr

Heat 'rans#er Coe##icient:

= > 4.% 74.@ 14. H.. equation

4./Where

> height of Juencher

= > 3eat Transfer Coefficient

o%u$e o# Quencher +

( > q 6 = ! D T 12T

H..equation /

Ca%cu%ation o# Height o# Quencher :

( > $ !

H..equation 0

Combining equations , / and 0 we get the height of the Juencher

( > q ! 4./6 4.% 7 4.@! 1 4. ! D T 12T

$ ! > q ! 4./6 4.% 7 4.@! 1 4. ! D T 12T

4./> q 6 4.% 7 4.@! 1 4. ! $

)utting all the values,

4./

> %.//%?

> "#.0% m

o%u$e o# Quencher:

( >$ ! K ( > ""0.4"? m%

9$



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DESIGN OF QUENCHER

7.11 )(ECI+IC'I*N )HEE':

I"enti#ication

Item Juencher

Item L J&"4"

Type 'pray Type

;o. of item "

+unction

Juenching the reactor outlet stream

0esign seci#ication7as inlet Temperature ##4 oC

7as outlet Temperature @/oC

1iquid inlet Temperature /oC

1iquid outlet Temperature 0/oC

8perating )ressure "A# *)a

esign Temperature %/4 oC

esign )ressure #44*)a

iameter %."? m

3eight "#.0% m

2aterial Carbon 'teel @" : /

(olume ""0.4" m%

Quenching $echanis$

Juenching media 3#'8%4 M-

Juenching 'ystems ;oles

9%


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Quencher TOWER Design