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Theme 4
Industrial environmental issuesFlue gas purification processes
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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)
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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
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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
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Proclamation in 1276
”Whosoever shall be found guilty of burning coal, shall suffer the loss of his head”
King Edward I
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Roster (moving grate) boiler
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“Plug-flow” boiler (PB)
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Atomspheric fluidized bed (AFBC)
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Circulating fluidized bed (CFBC)
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Pressurized fluidized bed (PFBC)
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Exampel of different cleaning technologies
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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
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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)
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Decision tree for emissions control
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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
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Residual products
• Waste-water• Solid waste• Sludge• By-products
Residual products might contain – Ash– Sulfur species– Nitrogen species– Chlorides– Heavy metals– Traces of organics
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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
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Trace metals
Content of trace metals in waste product from desulfurization process based on spray drying. Major constituents are calcium sulfite and fly ash.
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Cyclones for particulate removal
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Electrostatic precipitators
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ESP Unit
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Baghouse filter
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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
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Spray-Dry Scubbing
• Spray-drying of a lime slurry
Ca(OH)2 + SO2 F CaSO3 + H2O
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Wet Flue Gas desulfurization Process
Typical Process schematic
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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!!!!
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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
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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
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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
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The FLOWPAC System
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The FLOWPAC Reactor
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The Karlshamn Plant
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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
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SCR Design
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How to operate an SCR
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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+
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PSA for a biogas plant
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The Chilled ammonia process
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Wet Amine based CO2 absorption
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Integrated systems
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Prescrubber and absorber
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The NID System
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SYSAV Flue gas cleaning