Theme 4

Industrial environmental issuesFlue gas purification processes

Schedule for Theme 4• Monday 25/11, 08.15 -- 10.00 (DC:Lhö):

– Lecture on “Flue Gas Cleaning” (Hans)• Tuesday 26/11, 10.15 -- 12.00 (Hall C):

– Lecture on “Gas-Liquid Reactions” (Hans)• Wednesday 27/11, 08.15 -- 10.00 (Hall C):

– Lecture on “Absorber design” (Hans)• Wednesday 27/11, 13.15 -- 16.00 (Seminar room L):

– Exercises demonstrated on whiteboard (Hans)– Note: Disregard Tasks 4.1 and 4.2– Presentation of compulsory task 4 (Anders)

• Thursday 28/11, 10.15 -- 12.00 (Seminar room L): – Try yourself, examination 2008 + exercise 4.5 (Hans)

• Friday 30/11, 13.15 -- 15.00 (Seminar room M):– Work with compulsory task (Anders)

Hand-outs for Theme 4

• PPT material on Flue gas cleaning• Absorption with chemical reaction– PPT material– Gas-Liquid Reactions (mini-compendium)– Absorber Design (mini-compendium)

• Solutions to exercises• Text description of compulsory task 4

Flue gas cleaning

Removal of gaseous and particulate polutants from flue gases generated by stationary combustion plants

• Coal or oil fired power plants• Gas turbines• Soda boilers• Biomass fired heating plants• Waste fired combustion plants

Flue gas cleaning is only one of generic technologies for emissions control

Proclamation in 1276

”Whosoever shall be found guilty of burning coal, shall suffer the loss of his head”

King Edward I

Roster (moving grate) boiler

“Plug-flow” boiler (PB)

Atomspheric fluidized bed (AFBC)

Circulating fluidized bed (CFBC)

Pressurized fluidized bed (PFBC)

Exampel of different cleaning technologies

Generic problems

• Combustion plants are not classified as traditional process industry

• Flue gas cleaning plants are based on technology emerged from the process industry

1. Utility companies require simple technology, the process industry uses complex technology but cheap feed-stocks

2. The utility industry requires 25 years of capital depreciation, the process industry 10 years at the most

Flue gas content

• Inert components– Nitrogen, water and oxygen

• Toxic components– Fly ash, trace metals, hydrocarbons, dioxines and POM

• Acidic species– Sulfur oxides (SO2, SO3), nitrogen oxides (NO, NO2) and

halogen acids (HCl, HF, HBr)

• Greenhouse gases– Carbon dioxide (CO2) and laughing gas (N2O)

Decision tree for emissions control

Feed-stocks and products• Principle: Pollutant + Reagent Product• Problem

– Cost of reagent– Secondary pollutants

• Alternatives:– Reagent

• Throwaway• Useful by-product• Becomes inert• Recycled• No reagent

– Pollutant• Throwaway• Useful by-product• Becomes inert

Residual products

• Waste-water• Solid waste• Sludge• By-products

Residual products might contain – Ash– Sulfur species– Nitrogen species– Chlorides– Heavy metals– Traces of organics

Removal of particulates

PRINCIPAL SOURCES OF PARTICULATES

• Ashes from the fuelMinerals, un-combusted, trace elements

– Bottom ash– Fly ash

• Reagents and productsCalcium compounds, etc.

• Generic removal principles – Cyclones– Wet scrubbers/Absorption towers– Electrostatic precipitators– Baghouse filters

Trace metals

Content of trace metals in waste product from desulfurization process based on spray drying. Major constituents are calcium sulfite and fly ash.

Cyclones for particulate removal

Electrostatic precipitators

ESP Unit

Baghouse filter

Flue-gas desulfurization• The Wellman-Lord Process

– Sulfuric acid, elemental sulfur or sulfur dioxide• The Walter Process

– Ammonium sulfate• The activated coke

– Sulfuric acid• Spray-Dry Scrubbing (Wet-Dry Scrubbing)

– Dry calcium sulfite• Dry injection

– Mixed product containing calcium sulfite• Wet FGD

– Gypsum or sludge of calcium sulfite

Spray-Dry Scubbing

• Spray-drying of a lime slurry

Ca(OH)2 + SO2 F CaSO3 + H2O

Wet Flue Gas desulfurization Process

Typical Process schematic

Wet Flue-Gas Desulfurization (WFGD)

• The process is based on a slurry of slaked lime • Ca(OH)2 + SO2 CaSO3 + H2O

– or• Limestone

• CaCO3 + SO2 CaSO3 + CO2

• Oxidation may occur• CaSO3 + ½ O2 CaSO4

• Limestone is a mineral that has to be ground, lime is obtained by calcination (heat requirement) of limestone and slaked by the use of water

• CaCO3 CaO + CO2

• CaO + H2O Ca(OH)2

Presently, the cost determines how reagent is selected!!!!

Schematic reaction mechanism

• Absorption step– SO2 + H2O HSO3

- + H+

– H+ + SO32- HSO3

-

• Limestone dissolution– CaCO3 + 2H+ Ca2+ + H2O + CO2

• Oxidation– SO3

2- + ½ O2 SO42-

• Precipitation– Ca2+ + SO3

2- CaSO3

– Ca2+ + SO42- CaSO4

Important design considerations• Oxidation or not?

– Natural oxidation– Forced oxidation– Inhibited oxidation

• Important parameters– Removal efficiency

• Scrubber design• Limestone grinding• Process chemistry and pH• Additives

– Scaling (incrust formation)• Scrubber design• Process chemistry and pH• Degree of oxidation

– Corrosion• pH• Materials of construction• Chloride content

– Cost• Scrubber size• Energy consumption

Additives and auxillaries• Additives

– Adipic acid– Magnesium ion– Thiosulfate or elemental sulfur– Sodium salts

• Auxillary equipment– Pre-quencher– Demister/Mist eliminator– Reheater– Grinder– Sludge treater

• Thickener• Filter system

The FLOWPAC System

The FLOWPAC Reactor

The Karlshamn Plant

Flue Gas Denitrification• Nitogen oxides coinsist of 95% NO and 5% NO2 from combustion processes. Fluidized beds

might generate some N2O

• The generic problem: NO has a low solubility and is not very reactive.

• Wet methods– Potasium permanganate– Sodium chlorite– Iron- EDTA

• Oxidation-Absorption– Pre-oxidation of NO to NO2 using ozone or chlorine dioxid

• Dry processes– The cupper oxide process– Alkalized alumina– Electron beam– Selective non-catalytic oxidation– Selective catalytic oxidation

SCR Design

How to operate an SCR

Carbon capture

• Pressure swing adsorption• Scrubbing with water• Chilled ammonia absorption• Absorption in aqueous amine systems• Leading system: MDEA and Piperazine– CO2 + A*H2O HCO3

- + AH+

PSA for a biogas plant

The Chilled ammonia process

Wet Amine based CO2 absorption

Integrated systems

Prescrubber and absorber

The NID System

SYSAV Flue gas cleaning