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Scrubbers Colloquium

25.11.15 N. Maximova and the class. Puu-0.4400

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Scrubbers Quiz

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1. Gas-Phase Contacting Scrubbers

I. In a venturi scrubber, the majority of pollutant removal occurs in the:

a. Converging section

b. Throat

c. Diverging section

II. A venturi scrubber in which liquid is introduced above the throat section:

a. Increases the likelihood of dust buildup on the throat

b. Reduces dust buildup on throat surfaces

c. Has the highest gas absorption capabilities of any wet collector

d. None of the above

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Gas-Phase Contacting Scrubbers

III. In general, venturis are more effective in removing ____________________ than they are in removing ____________________.

a. Gases, particles

b. Particles, gases

IV. Venturi scrubbers are useful for simultaneous gas and particle removal, especially when:

a. Scale buildup could be a problem

b. A high concentration of dust is in the exhaust stream

c. The dust is sticky or has a tendency to plug openings

d. The gaseous pollutant is very soluble

e. All of the above

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Gas-Phase Contacting Scrubbers: Answers

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b. Throat

In a venturi scrubber, the majority of pollutant removal occurs in the throat.

II

b. Reduces dust buildup on throat surfaces

A venturi scrubber in which liquid is introduced above the throat section reduces dust buildup on throat surfaces.

III

b. Particles, gases

In general, venturis are more effective in removing particles than they are in removing gases.

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Gas-Phase Contacting Scrubbers: Answers

IV.

e. All of the above

Venturi scrubbers are useful for simultaneous gas and particle removal, especially in the following situations:

• Potential problem of scale buildup

• A high concentration of dust is in the exhaust stream

• The dust is sticky or has a tendency to plug openings

• The gaseous pollutant is very soluble

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2. Liquid-Phase Contacting Scrubbers

I. In a spray tower, the ____________________ the droplet is, the higher the theoretical collection efficiency will be.

a. Smaller

b. Larger

c. Higher

d. Lower

II. In a spray tower, gas collection can be increased by increasing:

a. The size of the liquid droplets

b. The liquid-to-gas ratio (L/G)

c. The gas velocity

d. All of the above

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Liquid-Phase Contacting Scrubbers

III. For ejector venturis, particle collection efficiencies increase with an increase in:

a. Nozzle pressure

b. Liquid-to-gas ratio (L/G)

c. Pressure drop

d. All of the above

IV. True or False? Because of their open design and the fact that they do not require a fan, ejector venturis are capable of handling a wide range of corrosive and/or sticky particles.

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Liquid-Phase Contacting Scrubbers: Answers

I: a. Smaller. In a spray tower, the smaller the droplet is, the higher the theoretical collection efficiency will be. However, if the droplets are too small and the gas flow up the tower is too fast, then the droplets can be carried out of the tower.

II: b. The liquid-to-gas ratio (L/G) In a spray tower, gas collection can be increased by increasing the liquid-to-gas ratio (L/G).

III: d. All of the above. For ejector venturis, particle collection efficiencies increase with an increase in: Nozzle pressure, Liquid-to-gas ratio (L/G), Pressure drop

IV: True. Because of their open design and the fact that they do not require a fan, ejector venturis are capable of handling a wide range of corrosive and/or sticky particles.

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3. Wet-Film (Packed Tower) Scrubbers

I. Packed towers are frequently used for removing gaseous pollutants because:

a. The packing provides a large surface area for gas-liquid contact

b. They have relatively low pressure drops compared to plate towers

c. The packing provides good mixing of gas and liquid and a long residence time

d. All of the above

II. A ____________________ packed tower cannot handle large variations in liquid or gas flow rates because flooding may occur.

a. Cocurrent

b. Countercurrent

c. Crossflow

d. Fiber-bed

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Wet-Film (Packed Tower) Scrubbers

III. True or False? Packed towers remove particulate matter and other solids more easily and with less maintenance problems than plate towers.

IV. In processes having high-temperature flue gas, ____________________ towers are more suitable because their internal components will expand and contract.

a. Plate

b. Packed

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Wet-Film (Packed Tower) Scrubbers: Answers

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d. All of the above

Packed towers are frequently used for removing gaseous pollutants for the following reasons:

The packing provides a large surface area for gas-liquid contact,

They have relatively low pressure drops compared to plate towers,

The packing provides good mixing of gas and liquid and a long residence time

II

b. Countercurrent

A countercurrent packed tower cannot handle large variations in liquid or gas flow rates because flooding may occur

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Wet-Film (Packed Tower) Scrubbers: Answers

III. False

Packed towers do NOT remove particulate matter and other solids more easily and with less maintenance problems than plate towers. The tops of plates can usually be accessed through openings, while the middle of the packed bed cannot.

IV. a. Plate

In processes having high-temperature flue gas, plate towers are more suitable because their internal components will expand and contract.

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Combination Devices - Liquid-Phase and Gas-Phase Contacting Scrubbers I. In a cyclonic spray scrubber, particles are primarily collected:

a. As they hit the wetted walls

b. As they impact the liquid droplets

c. Due to gravity

d. In the throat

II. What are cyclonic scrubbers used most often to control?

a. Micrometer-sized particles

b. Large-sized particles

c. Gaseous emissions

d. Particles and gases simultaneously

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Combination Devices - Liquid-Phase and Gas-Phase Contacting Scrubbers III. In mobile-bed scrubbers, gas velocities are much ____________________ than in packed

towers or plate towers; therefore, mobile-bed scrubbers can be much____________________ in size.

a. Lower, smaller

b. Lower, larger

c. Higher, smaller

d. Higher, larger

IV. Gas absorption in mobile-bed scrubbers can be enhanced by:

a. Increasing the L/G ratio

b. Adding more packing height

c. Adding stages

d. All of the above

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Combination Devices - Liquid-Phase and Gas-Phase Contacting Scrubbers: Answers

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b. As they impact the liquid droplets.

In a cyclonic spray scrubber, particles are primarily collected as they impact the liquid droplets.

II

b. Large-sized particles

Cyclonic scrubbers are used most often to control large-sized particles.

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Combination Devices - Liquid-Phase and Gas-Phase Contacting Scrubbers: Answers III

c. Higher, smaller

In mobile-bed scrubbers, gas velocities are much higher than in packed towers or plate towers; therefore, mobile-bed scrubbers can be much smaller in size.

IV

d. All of the above

Gas absorption in mobile-bed scrubbers can be enhanced by the following:

Increasing the L/G ratio

Adding more packing height

Adding stages

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4. Dry Scrubbing Systems

I. In general, higher acid gas removal efficiencies are achievable as the operating temperature of the dry scrubbing system:

a. Increases

b. Decreases

c. Does not change

d. All of the above

II. The primary maintenance problem with dry scrubbing systems is:

a. Plugging in the sorbent transport system

b. Scaling

c. Corrosion

d. Erosion

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Dry Scrubbing Systems

III. For a given system design, what is the alkaline sorbent feed rate a function of?

________________________________________ and

________________________________________

IV. The amount of water that can evaporate in a spray dryer is dependent on the:

a. Acid gas levels

b. Sorbent type

c. Incoming temperature

d. All the above

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Dry Scrubbing Systems: Answers

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b. Decreases

In general, higher acid gas removal efficiencies are achievable as the operating temperature of the dry scrubbing system decreases

II

a. Plugging in the sorbent transport system

The primary maintenance problem with dry scrubbing systems is plugging in the sorbent transport system.

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Dry Scrubbing Systems: Answers

III

Incoming acid gas levels

Removal rate

For a given system design, the alkaline sorbent feed rate is a function of the incoming acid gas levels and removal rate .

IV

c. Incoming temperature

The amount of water that can evaporate in a spray dryer is dependent on the incoming temperature.

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5. Flue Gas Desulfurization (Acid Gas Removal) Systems

I . ____________________-based slurries absorb SO2 better than ____________________; however, the former are much more expensive.

a. Sodium, lime or limestone

b. Lime or limestone, sodium

c. Gypsum, lime or limestone

d. Limestone, lime

II. Which problem/problems must be considered when trying to remove both SO2 and fly ash in the same scrubber?

a. Pressure drops are higher

b. The scrubbing liquid, if recirculated, can contain a high level of fly ash

c. SO2 absorption efficiency is normally lower

d. All of the above

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Flue Gas Desulfurization (Acid Gas Removal) Systems

III. Spray towers on most FGD systems require higher ____________________ (for equivalent SO2 removal) than other absorber designs.

a. Pressure drops

b. Gas velocities

c. Liquid-to-gas ratios

d. All of the above

IV. True or False? The chemistry for SO2 removal in a limestone slurry is very different from that for SO2 removal in a lime slurry.

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Flue Gas Desulfurization (Acid Gas Removal) Systems

V. Regenerable FGD processes generate a saleable product such as:

a. Sulfur

b. Sulfuric acid

c. Gypsum

d. All of the above

VI. At high pH values, the scrubbing liquid in the sodium systems absorbs

____________________ and can form carbonate scale.

a. SO2

b. CO2

c. O2

d. CaCO3

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Flue Gas Desulfurization (Acid Gas Removal) Systems: Answers

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a. Sodium, lime or limestone

Sodium-based slurries absorb SO2 better than lime or limestone; however, the former are much more expensive.

II

d. All of the above

Problems that must be considered when trying to remove both SO2 and fly ash in the same scrubber are:

Pressure drops are higher

The scrubbing liquid, if recirculated, can contain a high level of fly ash

SO2 absorption efficiency is normally lower

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Flue Gas Desulfurization (Acid Gas Removal) Systems: Answers III

c. Liquid-to-gas ratios

Spray towers on most FGD systems require higher liquid-to-gas ratios (for equivalent SO2 removal) than other absorber designs. More liquid is used in spray towers because they have limited contact area available for absorption.

IV

False

The chemistry for SO2 removal in a limestone slurry is very similar to that for SO2 removal in a lime slurry.

V

d. All of the above

Regenerable FGD processes generate a saleable product such as: Sulfur, Sulfuric acid, Gypsum

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b. CO2

At high pH values, the scrubbing liquid in the sodium systems absorbs CO2 and can form carbonate scale.

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6. Design Evaluation of ParticulateWet Scrubbing Systems

I. Two important parameters in the design and operation of wet scrubbing systems that are a function of the process being controlled are:

a. Static pressure drop and collection efficiency

b. L/G ratio and pressure drop

c. Dust properties and exhaust gas characteristics

d. Liquid flow rate and L/G ratio

II. True or False? Particle size distribution is the most critical parameter in choosing the most effective scrubber design and determining the overall collection efficiency.

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Design Evaluation of ParticulateWet Scrubbing Systems

III. True or False? Efficient particle removal requires low gas-to-liquid (relative) velocities.

IV. Which of the following factors affect the pressure drop of a scrubbing system?

a. Scrubber design and geometry

b. Gas velocity

c. Liquid-to-gas ratio

d. All of the above

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Design Evaluation of ParticulateWet Scrubbing Systems: Answers

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c. Dust properties and exhaust gas characteristics

Two important parameters in the design and operation of wet scrubbing systems that are a function of the process being controlled are dust properties and exhaust gas characteristics.

II

True

Particle size distribution is the most critical parameter in choosing the most effective scrubber design and determining the overall collection efficiency.

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Design Evaluation of ParticulateWet Scrubbing Systems: Answers

II

False

Efficient particle removal requires high gas-to-liquid (relative) velocities.

IV

d. All of the above

The following factors affect the pressure drop of a scrubbing system:

Scrubber design and geometry

Gas velocity

Liquid-to-gas ratio