Rotary Kiln Technology for Hazardous Waste Incineration
Presentation
CTU –Conzepte Technik Umwelt AG
Switzerland
Contents
?Introduction
?Rotary Kiln Combustion
?Kiln features
?PCC Combustion / bottom ash removal ?Heat recovery
?Noxious compounds –and their removal ?Conclusions
Introduction
?Rotary kiln considered as ?dinosaur‘of incineration, since accepting more or less all kinds of hazardous wastes like
–Solids
–Pastes/slurries
–Liquids
–Gases
?Rotary kiln incineration has a long tradition
?In the late1980ies and 1990ies the technology leaped forward again by
–Introducing larger post combustion chambers
–Higher temperature
–Improved flue gas cleaning
Combustion–rotary kiln
?Introduction of waste through front wall
?Auxiliary flame for ignition and additional PCI (if required)
?Air addition in order to keep sufficient oxygen excess ?Temperature control depending upon waste(min. 800°C, m ax.
1200°C
? 2 operating modes possible:
–Slagging: slag becomed pasty to liquid high temperature, high wear
–Non slagging: slag remains solid sinter lower temperature, lower wear
Rotary kiln–critical points
?Front wall: sealing to kiln important air control
?Front wall:
–needs to accomodate all product introductions
–burner(s)
–solids feeds(slide, screw conveyers, others)
–gaseous feeds(nozzles) etc.
?Joint to PCC:
–sealing important(air flow control)
–Cooling of hot end important(steel is exposed to PCC temperature)?Refractory Material
–Selection important depending also on waste composition
–High wear resistance important
–Brick material for easier replacement
Front Wall from kiln side
Front wall / kiln/ joint to PCC
Rotary Kilns–Sizes, geometry
?Largest size: limited by mechanical reasons(bricks) approx. 4.5m inner diameter approx. 60.000 tpa ?Lowest size: limited by access for brick replacement
1.4m inner diameter approx. 6.000 tpa
?Length: CTU‘s design: 8 -10m depending on size ?Inclination: 1°
?Speed: 0.5 to 2 rpm depending on waste material (ignition, size etc.)
Post Combustion
?Important in order to terminate combustion on gas side
?Acts as a separator of gas and slag/bottom ash
?Auxiliary burners to reach temperature(EU-regulation: 1100°C,
2 sec residence time)
?Chamber circular in order to improve mixing of air/unburnt gas ?Refractory not as critical in upper part, critical in lower part (liquid slag/bottom ash)
?Auxiliary fuel may be waste liquid with high PCI
Bottom Ash removal
?Ash Cooling using water
–Easier removal smaller pieces
–Water acts as seal
–most common system today
Heat Recovery
?Classical waste recovery boiler
?Special parameters for hazardous waste
–Steam parameters limited
–Temperature between radiation and convection section of large importance
–Spacing of convection tubing of high importance
–Steam blowing of importance
?Design upon intended use of steam
–Electrical power production
–Saturated steam for process use
–Mixed heat/power application
Noxious compounds and their removal ?Noxious compounds originate mainly from waste:
–Halogens (Cl, F, Br, I)
–Sulfur
–Heavy metals (Hg, Pb, Cd, Cr, Ni etc.)
–Dust
?Few are produced by combustion or in downstream systems –NOx: mainly from combustion of nitrogen containing waste
–Dioxins/furans: de-novo-synthesis during cool down
?Removal today not problematic anymore! Very low limits can be achieved using up to date technology
Noxious compounds and their removal
?Dust removal as first step
–Today‘s electrostatic preciopitators or bag houses fulfill all requirements
–Combined dioxin removal possible by char coal addition
–Most heavy metals efficiently removed
Bag house in haz
waste plant
Noxious compounds and their removal ?Todays achievements:
?Dust emissions:< 5 mg/Nm3?Carbon Monoxide< 50 mg/Nm3?Total VOC< 10 mg/Nm3?Hydrochloric acid:< 5 mg/Nm3?Fluoric Acid:< 1 mg/Nm3?Sulfur dioxide< 25 mg/Nm3?Mercury / Cadmium< .05 mg/Nm3?Dioxins/Furans< .1 ng/Nm3?NOx< 70 mg/Nm3