Industrial environmental issues Flue gas purification processes Theme 4 Industrial environmental issues Flue 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 Utility companies require simple technology, the process industry uses complex technology but cheap feed-stocks The utility industry requires 25 years of capital depreciation, the process industry 10 years at the most

Flue gas content Inert components Toxic components Acidic species 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

Residual products Residual products might contain 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 fuel Minerals, un-combusted, trace elements Bottom ash Fly ash Reagents and products Calcium 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 SO32- + ½ O2  SO42- Precipitation Ca2+ + SO32-  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) Degree of oxidation Corrosion pH Materials of construction Chloride content Cost Scrubber size Energy consumption

Additives and auxillaries 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