Spray

AIR POLLUTION CONTROL TECHNOLOGY (CEB 30403)

TITLE OF EXPERIMENT

PARTICULATE EMISSION CONTROL BY SPRAY CHAMBER

NAME : THEYVAN A/L GANESAN

ID : 55201212141

LECTURER : DR. AMELIA

DATE OF EXPERIMENT : 2 MARCH 2015

Page | 1

1.0 INTRODUCTION

This expermient was conducted to analyse the effect of droplet size upon separation efficiency of

the spray chamber unit, by using different nozzle. Spray chambers are categorized as an example

of wet scrubber which performs air pollution controlling. 300 gram of kaolin was used as sample

to study the particulate collection efficiency of spray chamber.

Spray chambers are useful in collecting particulate matter. The devices uses spray nozzles to

atomize the liquid. Particles collide with the droplets and are entrained. Because the simple

design of the system, the scrubbing liquid can be recycled and still be effective, even with

relatively high suspended solids concentrations. A mist eliminator is necessary for this type of

device (Gayle,1999).

Some relative motion is necessary for the particle and liquid gas interface to come in contact. In

spray chamber, this motion is provided by spraying the droplets through the gas so that they

impinge on and make contact with the particles (Daniel,2008).

Figure 1.0 : Countercurrent Spray Chamber

(Source : David, Air Pollution, 2000,pg.140)

Page | 2

Spray chambers are low efficiency collectors of coarse particles. Figure 1.0 illustrates

countercurrent spray tower, in which the liquid droplets are produced by spray nozzles or

atomizers and the flue gas enters the tower through a perforated distribution plate at the base of

the tower (Richard,1994). To avoid entrainment and carry over of water droplets, the velocity of

the spray water droplets must exceed the gas velocity 2 to 5 feet per second (1-2 m/s). The higher

this velocity difference, the better the collection efficiency (Bela, 1991).

The pressure drop on the gas side of the countercurrent spray chamber is usually less than 250 Pa

and it’s dust collection efficiency is under 80 % for all but the coarsest dust particles (over 10

microns in diameter).

The collection efficiency of spray chamber is normally analysed by Kleinschmidts equation,

No = 1 – e-fE

Where,

N0 = Overall collection efficiency

f = Fraction of inlet gas/air swept by the drop

E = Particle collection efficiency of a single droplet

Page | 3

2.0 OBJECTIVES

This experiment was conducted to achieve the following objectives :

To determine the effect of droplet size upon separation efficiency of the spray chamber

unit, by using different nozzle.

To study the operating principle of spray chamber.

To study the ability of spray chamber in removing pollutants.

Page | 4

3.0 METHODOLOGY

No. Descriptions

1 All valves are initially closed except valve V9 to be initially opened.

2 The Centrifugal Pump, P1 was switched on.

3 Depending on the nozzle to be tested, the isolation valve as outlined in Table 1

below was opened. Then, the appropriate control valve was adjusted so that the

nozzle pressure, PT1, was set according to Table 1.

Table 1.0: Operation Guide for AP03 Spray Chamber System

Page | 5

NozzleDroplet

Size

(µm)

Isolation

valve

Set

Pressure,

PT1

Flowmeter Control Valve

N1 520 V1 2bar FM1 CV1

N2 290 V2 2 bar FM2 CV2

4 The nozzle water flow rate of flow meter FM1 was recorded for nozzle size of

520 µm for first test and followed by 290 µm nozzle for second test.

5 Valve V9 was closed. The water level inside the spray chamber was increased

until it reached the desired level indicated by the line on the chamber. Once so,

the valve V9 was adjusted to maintain this water height.

6 The air blower speed controller was set to its minimum. The blower was switched

on. Then, the air blower speed controller was gradually adjusted so that the

blower frequency is set to 20.0Hz.

Page | 6

7 300 gram of Kaolin was sieved and weighted.

8 300 g of Kaolin was poured into the feed vessel with the feed control valve, V11

fully closed. Then, control valve V11 was opened slightly so that the sample flow

down steadily.

Page | 7

9 After all the sand had been delivered into the air stream, wait two minutes to

ensure all dust has cleared from the pipeline then the centrifugal water pump P1

and Centrifugal Air Blower was switched off.

10 Valve V9 was slowly opened to let the dust-laden water in the spray chamber

flow down by gravity to dust collecting bucket.

11 The dust was let to settle down in the bucket (approximately 5 minutes) once all

water has flowed down from the chamber.

Page | 8

12 The bucket was taken out carefully. The excess water was drained. Then the dust

was collected on a suitable oven tray. The wet sample was heat up in an oven at

200ºC for 2 hours until the sample becomes sufficiently dry.

12 The collected sample was weighted and the final weight was recorded.

4.0 DATA & RESULTS

Table 2.0: Nozzle size - 520µm ( Nozzle 1, N1 )

Set Pressure, PT1 (Bar) 2

Air blower speed (Hz) 20

Weight of sample loaded (g) 300g

Weight of sample collected (g) 295g

Collection efficiency, η (%) 98.33%

Table 3.0: Nozzle size - 290µm ( Nozzle 2, N2 )

Page | 9

Set Pressure, PT1 (Bar) 2

Air blower speed (Hz) 20

Weight of sample loaded (g) 300g

Weight of sample collected (g) 250g

Collection efficiency, η (%) 83.33%

5.0 DISCUSSION

This experiment was performed to determine the effect of droplet size upon separation efficiency

of the spray chamber unit by using different nozzle. There are two type of nozzles inside the

chamber to produce two different droplet sizes. Nozzle size of 290µm and 520µm was tested to

study the objective of the experiment where it was tested one after another.

During the experiment, 300g of sample of kaolin was weighed and put into the feeder. For the

first test, nozzle N1 with droplet size of 520 µm was tested for its collection efficiency. The

collected particulate matters for the first test is 295g. As for the second test, the nozzle N2 with

droplet size of 290 µm was tested. The result of particlulate matters collected by using N2 was

250g. The spray chamber efficiency was calculated via using the formula below:

Page | 10

Efficiency,η=weight of sample collected

weight of sample loaded×100 %

Based on the readings recorded in Table 2.0 and Table 3.0, the efficiency of nozzle size of 520

µm is 98.33 % and 83.33 % for nozzle size of 290 µm. It is obiviously reveals that the

collection efficiency of nozzle size of 520 µm is higher than nozzle size of 290 µm. But this

result is actually oppose the theory, where the nozzle with bigger size should give least

collection efficiency compared to the smallest one. Since this experiment came out with

different results, it can be said that some factors was affected the operating mechanism of

spray chamber.

The first obivious error observed during the experiment is the air blower frequency was

37.69 Hz. According to the procedure, the frequency should be 20 Hz. The differences are

much larger. So, the speed of air blower might affected the efficiency of spray chamber.

The next error observed was, the unstable air flow rate. The air flow rate observed during the

experiment was 0.049 m/s but it is not stable. This might affected the velocity of air flow rate

in nozzles. The pluggings in nozzles also might contributed for this error. If the nozzle is not

cleaned for a long time this situation will happen.The combination of unstable air flow rate

and pluggings in nozzle surely affected the operation of spray chamber.

Spray towers have low power consumption but have relatively low particulate collection

efficiencies. The recirculated water in the system must be thoroughly cleaned to prevent

excessive nozzle fouling or clogging. Nozzle cleaning and replacement are a major part of the

maintenance required for these units.

Page | 11

In spray towers or spray chambers, gas streams are fed into a chamber and contacted with

scrubbing liquid produced by spray nozzles. The droplet size is controlled to optimize particle

contact and droplet separation from the gas stream. Chambers can be oriented for cross-flow,

countercurrent flow, or concurrent (co-current) flow. Chambers may also include baffles to

improve gas-liquid contact.

The collection efficiency of spray chamber can be relate to the Kleinschmidts equation :

No = 1 – e-fE

Where,

N0 = Overall collection efficiency

f = Fraction of inlet gas/air swept by the drop

E = Particle collection efficiency of a single droplet

According to this equation, the collection efficiency is directly proportional to the fraction (f) of

inlet gas /air swept by the drop and particle collection efficiency of a single droplet, E . Increase

of f and E will increase the collection efficiency. Fraction f and E can be describe in following

equation:

f = 6.12 x 10 4 H.F L

DFG

H = Distance of the droplet travels with respect to incoming gas/air

FL = Liquid flow rate

FG = Incoming Gas/air flow rate

D = Droplet diameter

Page | 12

The smaller the droplet diameter and incoming gas/air flow rate, the higher the fraction of inlet

gas/air swept by the drop. The higher the distance of the droplet travels with respect to incoming

gas/air and liquid flow rate, the higher the fraction of inlet gas/air swept by the drop.

E = ( Y 0 + rp) 2

Rd2

Y0 = the initial Y position measured from drop centerline of the particle center trajectory that just

graze the droplet

rp = particle radius

Rd = droplet radius

The smaller the droplet radius, the higher the particle collection efficiency of a single droplet and

vice versa. Hence, the nozzle size 290 µm must give higher collection efficiency compared to

520 µm.

Spray chamber is an inexpensive pollution control device. It is effectively remove large

particles and highly soluble gases. But, may create water (or liquid) disposal problem and

relatively inefficient at removing fine pollutants.

6.0 CONCLUSION & RECOMMENDATION

This experiment was conducted to analyse the effect of droplet size upon separation efficiency of

the spray chamber unit, by using different nozzle. The data and result collected revelas that the

efficiency of spray chamber by using nozzle N1 ( 520 µm ) was 98.33 % while for nozzle N2

( 290 µm ) was 83.33%. Therefore, this experiment concluded that a larger droplet size have a

greater collection efficiency compared to a smaller droplet size. However, this result does not

the obey the theory and the result considered as fault due to some errors. The errors such as

Page | 13

plugging in nozzle, inaccurate air blower frequency and unstable air flow rate affected the

overall operation and performance of spray chamber.

As for recommendation, it is suggested that the nozzle must have to clean regularly to avoid any

pluggings in it. The air blower speed controller must have to undergo inspection to obtain the

desired frequency during the actual experiment. The air flow meter also have to inspect regularly

or need to substitute with new air flow meter if it malfuncition, where it could give a stable air

flow rate reading.

7.0 REFERENCES

1) Richard, (1994), Fundamentals of Air Pollution, California, Academic Press Inc.

2) Gayle, (1999), Hazardous Materials and Hazardous Waste Management,Canada,John

Wiley & Sons Inc.

Page | 14

3) Bela, (1991), Municipal Waste Disposal in the 1990s,Penyslavania, Chilton Book

Company.

4) Daniel,(2008), Fundamentals of Air Pollution,California,Elseveir Inc.

5) David,(2000), Air Pollution,Florida,CRC Press LLC.

8.0 APPENDIX

Efficiency of spray chamber were calculated using the formula below:

Efficiency,η=weight of sample collected

weight of sample loaded×100 %

Page | 15

i. NOZZLE N1 (520 µm droplet size):

Efficiency,η=295

300×100 %

= 98.33 %

ii. NOZZLE N2 (290 µm droplet size):

Efficiency,η=250

300×100 %

= 83.33 %

Page | 16

Figure 2.0: Raw data of spray chamber system

Page | 17