Combustion Products and Emission Controls CHE 450

Combustion C x H y +(x+0.25y)*(O N 2 )=xCO yH 2 O+3.76(x+0.25y)N 2 Ex: CH 4 + 2(O N 2 ) = CO 2 + 2H 2 O N 2

Combustion Pollutants Particulate Matter (PM) SOx NOx CO-usually not an issue with large, well- controlled power plants CO 2

PM Particulate Matter-very small diameter solids or liquids suspending in gases. (ash/soot/gas conversion). PM 10, PM 2.5 >10 um-nasal passage/mucus <0.1 um-bronchial tree/mucus 0.1<10 um-respiratory problems

PM – Gravity Settler/Cyclone – Fabric Filter/Baghouse – Electrostatic Precipitator – Wet scrubbing

Fabric Filter Shaker

Fabric Filter

ESP Use electric field to attract PM “Negative Corona” – Strong E-field generates high energy electrons – Electrons create ionized gas species – Ions are absorbed onto particles – Particles absorb onto plates

ESP

Advantages – High Efficiency – Low pressure drop – Low operating costs Disadvantages – High capital costs – Large – Not flexible to changes in operating conditions

Sulfur SO 2 (and some SO 3 ) is emitted SO 2 oxidized to SO 3 in atmosphere SO 3 + H 2 O = H 2 SO 4 = ACID RAIN

Sulfur Pre-combustion or post combustion Most common: limestone scrubbing CaCO 3(s) +H 2 O+2SO 2 = Ca 2+ +CO 2 + 2HSO 3 - CaCO 3(s) +2HSO Ca 2+ =2CaSO 3 +CO 2 +H 2 O

SOx Scrubbing

Nitrogen High Temps: NO, NO 2 formed 95% of stationary source NOx is NO Thermal NOx, Fuel NOx Brownish color In combination with VOCs, form O 3

Nitrogen O +N 2 →NO+N N+O 2 →NO+O N 2 +O 2 →2NO K~10

Nitrogen SCR=Selective Catalytic Reduction ˚C ~80% effective 4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O 2NO 2 + 4NH 3 + O 2 → 3N 2 + 6H 2 O NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O

SCR

Carbon Capture and Storage

Capture Use temperature swing to absorb/desorb

Storage Reduces delivered electricity by at least 25%

The Thermodynamic System The System Contains some energy, E The Surroundings (i.e., the rest of the Universe…)

First Law – Conservation of Energy “energy can be converted from one form to another but cannot be created nor destroyed” 1 2 Q W

“Enthalpy” - H Enthalpy measures total energy of the system. Internal energy (energy required to create system) Energy required to make room for it by displacing its environment: function of volume and pressure

PV and work In general, work is given by PV P V 1 2 B A Question: is work done by path A same as by path B? Work done depends on path taken! d signifies an exact differential  signifies an inexact differential

Second Law – Quality of Energy Decreases “energy flows from a higher potential (higher quality) to lower potential” Q W High TLow T Q A couple other statements of this: Clausius: No process is possible whose sole result is the transfer of heat from a body of lower temperature to a body of higher temperature Kelvin: No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work

“Entropy” - S Entropy measures “disorder” of the system. (“quality”) For a “reversible process” “reversible process” ≡ process that can be carried out and reversed without leaving traces on the surroundings

Reversible Systems For a reversible process involving heat transfer at T 0,

Irreversible Systems Clausius inequality: T S 1 2

Isentropic Compression Isothermal Expansion Isentropic Expansion Isothermal Compression Carnot Cycle

Heat Engine Want colder T cold and hotterT hot

Carnot Cycle Isothermal Expansion Isentropic Expansion Isothermal Compression Isentropic Compression

Brayton Cycle