Prof. ing. Marco Ragazzi Department of Civil and Environmental Engineering, University of Trento
Municipal Solid Waste as is MSW residual of selective collection under-sieve and over-sieve from MSW mechanical selection Sewage sludge
Exothermy from Biochemical oxidation Thermal drying Micro-wave drying Infrared drying Conditioning and mechanical dewatering
70 60 50 40 160% 140% 120% 100% Bio-drying 80% 60% One stream humidity 40% 20% 0% Bio-stabilization IN OUT IN OUT volatile solids Step Run I - with Bio-drying 50% org. LHV (t=0) LHV biod. LHV tot. m MSW (t=0) Probe 1 Probe 2 Probe 3 Probe 4 humidity volatile solids humidity volatile solids humidity vol.solids inert inert inert inert Max temp. ( C) Min temp. ( C) 40% (for minimum 30 3 days) Humidity (%) Oxygen 0% (% 0 v/v) 70 55 >50% >10% signif. >10% 70 55 Thermal drying IN humidity volatile solids inert 105 55 - OUT 0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 408 432 456 480 504 528 552 576 600 624 648 672 696 % 30 20 10 0 0 24 48 72 96 120 144 time 168 [h] 192 216 240 264 288 312 time [h] 60% 50 40 20 20% 10 Run with 8% org. Step II - Bio-stabilization LHV (t=0) LHV bioes. LHV tot. m MSW (t=0) Probe 1 Probe 2 Probe 3 Probe 4 VS consumption = 30 gvs/kgmsw VS consumption >> 30 gvs/kgmsw VS consumption = 0 gvs/kgmsw 120% (no water addition) 90 (with water addition) (no water addition) Bio-drying 100% 80 Two streams undersieve - Parameters of 70 process Bio-stabilization Bio-drying 80% 60 2 weeks Thermal Drying Waste Sludge not signif. Bio-drying 1 month 250 % C Bio-stabilization Thermal drying Two streams oversieve C 55 not signif. 0 24 24 48 48 72 96 72 120 144 96 168 120 192 144 216 240 168 264 192 288 312 216 time [h] [h] ++ + -
MSW bio-drying many operating plants no auxiliary fuel needed for drying volume available for temporary waste storing reduction of mass to be transported in case of decentralized treatment treated waste suitable for inert, metals and glass separation at high efficiency increase of LHV for RDF production or for modifying the characteristics of waste MSW thermal drying easy regulation of the humidity (and therefore of the LHV) of the treated waste final humidity lower than 10% (good temporary stability) short duration of the process (of the order of the hours) and quickness of starting possibility to work with an high process air recycling (oxygen is not limiting) suitability for over-sieve from automatic selection of MSW SEWAGE SLUDGE thermal drying useful for reducing transportation costs useful as a pre-treatment for combustion options (incineration, co-incineration, cement works) technology fully developed possibility to use high temperature
MSW bio-drying flies generation long duration of the process (at least 1 2 weeks) limited possibility of regulation of the humidity and of the LHV of the treated waste impossibility to get humidity lower than 10% impossibility to work with an elevated recycling of the process air because of the role of oxygen significant process air flow-rate to be treated consumption of volatile solids no longer available for energy generation MSW thermal drying necessity of auxiliary fuel in case of decentralized applications low temperature of process air (max 100 C) to avoid softening of plastics and ignition phenomena high flow-rates of process air to be treated necessity of auxiliary fuel in case of decentralized treatment high consumption of thermal energy for unity of mass of evaporated water absence of a volume of temporary storage few applications of this type in fittings in continuous operation SEWAGE SLUDGE thermal drying storage problems in case of very low humidity values
MSW bio-drying design criteria operation criteria bio-chemical / energy modeling MSW thermal drying - SEWAGE SLUDGE thermal drying option already optimized from the energy point of view
MSW bio-drying previsional bio-drying modeling emission factors to air solutions for process air recycling sewage sludge co-drying role of height emission release MSW thermal drying emission factors to air solutions for process air recycling role of height emission release SWEAGE SLUDGE thermal drying emission factors to air for micro-pollutants role of height emission release
Contribution to the development of a strategy alternative to direct combustion Useful also for small decentralized msw generation basins
Lowering the environmental impact could increase the cost of these options Adding air treatment units to the simple biofilter,, with a final stack, could make locally less acceptable these options
----------------------------------------------------------------------------------------------------------------------------------- ------------------------- marco.ragazzi@ing.unitn.it Department of Civil and Environmental Engineering, University of Trento