Removal Of Emissions At The Source

Question 1

how many ways can emissions be removed at the source, state them.

Answer 1

3 main ways .
Before combustion , during combustion and after combustion.

Question 2

How can emissions be removed before combustion?

Answer 2

Fuels can be pretreated to reduce content of N, S, H2O and trace elements. Oil refineries can do this to optimize combustion.

Question 3

How can emissions be removed during combustion?

Answer 3

This can only be done by optimizing combustion conditions. This will reduce the formation of CO,soot,NOx, CxHyOz.

Question 4

How can emissions be removed after combustion?

Answer 4

Emissions can be captured and treated.
Through Catalytic cleaning here additional chemical reactions are created with catalysts to reduce the presence of CxHyOz(hydrocarbons) , soot and NOx.
Filters can be put in to trap particles.

Question 5

Give examples of pretreatment of fuels(before combustion).

Answer 5

Sulfur can be removed from coal physically , biologically,and chemically.
Sulfur can removed from oil by undergoing heat treat process at the refinery.

Question 6

How do we optimize combustion conditions to reduce the formation of CO,NOx, CxHyOz(hydrocarbons) and soot.

Answer 6

This can be done by ensuring that there is enough oxygen , controlling air/fuel ratio, having adequate residence time in combustion chamber, regulating temperature .
Ensuring compatibility between fuel properties and combustion unit design.
Ensuring proper handling of combustion equipment.

Question 7

Give a description of how sulfur can be removed after combustion.

Answer 7

There are a number of proven technologies but the mostly commonly used one is Wet scrubbers.

This technology removes 90% of the sulfur and is affordable as 1 tonnofcSO2 costs between $00 to $500.

Question 8

Give a description of how combined sulfur and NOx removal works.(after combustion)

Answer 8

This can be done using the SNOX process.
Here a catalytic react can be used to NO to N2 using NH3.(collected and repurposed)
A catalytic reaction is used to oxidize SO2 to be come SO3, this then later combines with H2O to become H2SO4(sulfuric acid).

Question 9

Describe how exhausts can be catalytically cleaned.

Answer 9

This can be done by additional oxidation and reduction as seen in the SNOX process.

NO can. Be reduced to N2 which can collected and repurposed.
Carbon, hydrocarbons and carbon monoxides can be oxidated.
C+O2 = CO2
CO + 1/2O2 = CO2
CxHy+ bO2 = CO2 + H2O

Question 10

How is catalytic cleaning of exhaust done in cars?

Answer 10

Exhaust fumes enter the exhaust, here reduction is done using platinum and rhodium and oxidation is done using platinum and palladium.
In between these steps the gas goes through a ceramic honey comb mechanism

Question 11

What are some of the particle removal mechanisms?

Answer 11

This is dependent on filtration mechanisms.
There are four main categories of filtration mechanisms:
Inertial impaction
Diffusion
Interception
Electrostatic attraction

Question 12

What is inertial impaction ?

Answer 12

This is when larger particles of the gas with high inertia are unable to follow the path of the curved gas stream and collide with the fibers of the filter trapping them. Usually possible with large particle sizes.

Question 13

What is interception?

Answer 13

This is when molecules of a gas come close to the filter but do not collide with them but are are captured by the fibers of the filter.

Question 14

What is diffusion?

Answer 14

This is when there is movement of particles from a higher concentration to a lower one. Here the small particles collide with gas molecules causing them to change direction randomly. This change causes them to collide with the filter and are captured by the fibers

Question 15

What is electrostatic attraction?

Answer 15

This is the use of an electric charge to attract particles to the filter medium.

Question 16

Is this statement true: the smaller the particle the easier it is to diffuse .

Answer 16

True

Question 17

Is this statement true or false: interception and inertial impaction works best when the particle sizes are bigger.

Answer 17

True

Question 18

Is this statement true or false: between particle size 0.1 and 0.2 efficiency dips in all mechanisms.

Answer 18

True

Question 19

Is this statement true or false : when the particle sizes are between 2.0 and 10 the are likely to sediment

Answer 19

True

Question 20

What are some of the particle removal technologies that put some the mechanisms into practice? Describe them?

Answer 20

Cyclones : here particles are circulating in the vortex the bigger particles cannot keep because of inertial impaction and sediment,(they are least expensive and recommended. To constricted as part of exhaust systems).
Baghouse filters: this is the most preferred , it also know as textile filters. Gas is blown into the bag house filter and the particles adhere to the filter medium (diffusion ) .
Electrostatic filter : when gas flows through electrostatic filters it encounters a series of layers with electric charges. As particles move through these layers they are are attracted by opposite currents and trapped by the filters.(captures small particles).
Packed bed wet scrubber : water is sprayed into the chamber and the particles collide with these H2O molecules and are easily

Question 21

What must every plant have ?

Answer 21

Every processing plant must have cyclones to collect bigger particles and then a much smaller and sophisticated one like wet scrubber , electrostatic filter and bag house filter to remove remains particles.

Question 22

What are the tree main strategies for reducing CO2 emissions from the energy system?

Answer 22

1. Using less energy
2. Using low carbon energy sources.
3. Using carbon containing fuels but using carbon capture and storage.

Question 23

What do you know about CCS (Carbon Capture and Storage)

Answer 23

Serial methods exist that make carbon capture and storage easier.

Using oxyfuel combustion where nitrogen is removed and only oxygen used making the end product only CO2 which is much easier for capture and storage.

If you don’t opt for oxyfuel after combustion you are likely to have CO2 and nitrogen then you would need a membrane filter to separate the carbon from the nitrogen because nitrogen is not easily stored.

Carbon dioxide scrubbing using amines, hydroxides and minerals.

The CO2 is normally stored as compressed gas.

Question 24

What are some considerations for the carbon capture and storage method?

Answer 24

1. These additional measures reduce plant efficiency by 10 - 40%
2. Only captures about 80 - 95% of carbon in the exhaust gas.
3. Increase electricity prices by approximately 30 -60%

Question 25

How is CO2 stored

Answer 25

CO2 preferably can be captured, transported and stored deep in the ocean where oil was previously drilled. The ocean has the highest carbon storage capacity.

Carbon can be captured and stored in leaf litter , woody biomass, leaf litter soils but not for a very long time and not large amounts.(arranged in the order of least amount and least time upward).

Captured carbon be used for enhanced oil recovery where . This is when captured CO2 is used in drilled oil holes to extract more oil. Dry small amount used but is more than what is used in woody biomass, soil and leaf litter.

Question 26

How does Bio energy with CO2 capture and storage (BECCS) to produce negative CO2emissions work?

Answer 26

Bio energy is produced from biofuels In the form of ethanol and biodiesel which is derived from plants (woody biomass, agriculture and crops). During the production of bio energy the Carbon dioxide is captured with CCS technology and stored under ground. This results in negative emissions because energy production does not result in CO2 emissions and the plants absorb atmospheric CO2.

Question 27

Advantages of CCS.

Answer 27

1. Can use well known sources and existing infrastructure.
2. Can be a politically accepted solution for countries with large coal mines like USA and china.
3. Can give negative CO2 emissions.

Question 28

Disadvantages of CCS

Answer 28

1.Is not a long term solution since fossil fuels and CCS storage potential are limited.
2. CO2 may leak from storages.
3. Investment in new CCS technologies may take away funds from the development of renewable resources.