PB389 Integrated Solid Waste Management Numfon Eaktasang, Ph.D. Thammasat University

Solid Waste Management generation Waste reduction and separation at the source Collection Transportation Separation, processing & transformation Disposal

Disposal Technologies Landfill Thermal treatment Biological conversion

Dumping on Land

Burial

Hog Feeding

Thermal Treatment Solid waste Ash + Gases + Vapor + Smoke + Soot + Energy (1°pollutant) (2°pollutant) “conversion of solid waste into gaseous, liquid, and solid conversion products, with the concurrent or subsequent release of heat energy”

Thermal Treatment Open burning Air pollution Smoke Dust Health risk Respiratory system Eye irritation GHGs

Thermal Treatment Agricultural waste

Thermal Treatment Incineration Air pollution control system Dust collection system Ash

Categorization of thermal processing Combustion Stoichiometric: with exactly the amount of oxygen (or air) needed for complete combustion excess-air: with oxygen in excess of the stoichiometoric requirements Gasification partial combustion of solid waste under substoichiometric conditions to generate a combustible gas containing carbon monoxide, hydrogen, and gaseous hydrocarbons. Pyrolysis thermal processing of waste in the complete absence of oxygen

What is incineration? Basic reaction of stoichiometric combustion For carbon C+O2 CO2 For hydrogen 2H2+O22H2O For sulfur S+O2 SO2 However, difficult to achieve complete combustion in stoichiometric condition practically. Excess air must be used to promote mixing and turbulence The use of excess air affects the temperature and composition of combustion products (called flue gases) Excess air increase: oxygen contents increase and temperature of combustion decrease Temperature of flue gas is important for odor control. Less than 800 OC -> may occur odor problem greater than 1,000 OC -> may minimize the emission of dioxins, furans, VOCs

Complete Combustion 3T’s of combustion Time Temperature Turbulence

Complete Combustion C6H10O5 + 6O2 6CO2 + 5H2O + (Energy 5,000 Btu/Ib) Theoretical combustion air (TA) C6H10O5 1 Ib  oxygen requirement (6 × 32)/162 = 1.2 Ib Theoretical air = 1.2 × (100/23) = 5.2 Ib Excess air (EA) = excess air to complete combustion Actual combustion air (AA) = total air to complete combustion AA = TA + EA

Complete Combustion Ex: Excess air 50% AA = 5.2 Ib + (0.5 x 5.2) AA = 5.2 + 2.6 AA = 7.8 Ib AA = TA + EA

Why is the SW incinerated? To reduce the volume and weight of SW 1/4 by weight, 1/15 by volume To remove the bad smell To decompose the hazardous materials heat of high temperature decompose the smelling and hazardous components

Where incinerated? Hikarigaoka Incineration plant Tokyo, Japan http://tokyo23.seisou.or.jp/koujou/0koujou_pic.htm http://www.osaka-etoko.ne.jp/special/ maishima/01_kankyo.html

How incinerated?

Incineration plant platform Incinerator NOx remover Baghouse Ash pit Gas cleaner (HCl, SOx, HM) Waste pit http://tokyo23.seisou.or.jp/23ku_seisou/index.html

Types of combustion systems Waste type or combustion system Commingled wastes: Mass-fired combustion systems Processed wastes: Refuse derived fuel (RDF) fired combustion system

Types of combustion systems Mass-Fired Combustion Systems

Types of combustion systems Refuse derived fuel (RDF) fired combustion system

Types of Incinerators Single chamber incinerator

Types of Incinerators Multiple chamber incinerator

Types of Incinerators Incinerator type Stoker grate combustion Fluidized bed combustion Rotary Kiln Small incinerator

Stoker grate combustion Most common in mass-fired combustion system Movement of waste through the grate system, mixing of the waste, and injection of combustion air. (RT=2hrs) Air comes from below thorough the grate. Ash falls down to the collection hopper to conveyer. Temp. 850-1,200 0 C Many variations of grates: travelling, rotating, reciprocating and rocking grates

Stoker grate combustion

Traveling Grates

Reciprocating Grates

Rocking Grates

Roller Grates

Stoker grate combustion Advantages-Disadvantages Temp. 850-1,200 o C Commingled wastes Various composition of wastes Efficiency – 85% 1,200 ton/day High investment and maintenance costs

Fluidized bed combustion (FBC) Consists of a vertical steel cylinder with a sand bed, a supporting grid plate, and air injection nozzle. When air is forced up, the bed fluidizes and expands up to twice its resting volume. FBC are quite versatile and can be operated on a wide variety of fuels. The bed material: plain sand, silica or limestone (CaCO3) Limestone can contribute to decrease SO2 emission

Fluidized bed combustion (FBC)

Fluidized bed combustion (FBC) Advantages-Disadvantages Temp. 600-1,000 o C Complete combustion Processed wastes Efficiency – 90% 25-100 ton/day Low investment and maintenance costs

Rotary kiln Rotary kiln is widely used for cement production and also used for industrial waste incineration, especially oily mud, tar, pitch, paint mud, dye waste, or plastics.

Rotary kiln

Rotary kiln Advantages-Disadvantages Two-chamber incinerator (Temp. 700 and 1,200°C) 480 ton/day Used for hazardous waste Commingled wastes Various composition of wastes Efficiency – 80% High investment and maintenance costs

Small incinerator There are many kinds of anti-dioxins emission incinerators invented in Japan. They are suitable for small scale waste treatment, not like uncontrolled combustion in open space. Typical small incinerator Dioxin-emission prevention type

Environmental Control Systems Gaseous and particulate emissions Solid residuals Liquid effluents

Air emissions Nitrogen oxides (NOx) Sulfur oxides (SOx) include NO and NO2 Source of NOx: Thermal NOx and fuel NOx Precursors of the phtochemical oxidants, acid rain and fog Sulfur oxides (SOx) formed by the combustion of fuel containing sulfur an eye, nose and throat irritant. Asthma, bronchitis, acid rain Carbon mono oxide (CO) formed when insufficient oxygen is present Headache, nausea, sudden death Particle matter (PM) Visibility reduction and effect to human lung Metals MSW usually has a higher metal concentration than coal or oil.

Air emissions Acid gases Dioxins (PCDDs) and Furans (PCDFs) Not only NOx and SOx, but also Hydrogen chloride (HCl), Hydrogen fluoride (HF) Iron corrosion, acid rain Dioxins (PCDDs) and Furans (PCDFs) 75 PCDD isomers and 135 PCDF isomers Some of them have been found to be among the most toxic substances in existence. (e.g. 2,3,7,8-TCDD) Polychlorinated dibenzodioxin Polychlorinated dibenzofuran 2,3,7,8-TCDD

Pollution control systems Particulate Electrostatic precipitators fabric filters NOx Source separation combustion controls flue gas treatment SOx and acid gas wet or dry scrubbing CO and HC control Combustion controls

Electrostatic precipitator first particle control device for MSW incinerators removing fine (<10mm) and very fine (<2mm) particles. Mechanism -20,000 to -100,000 V, applied to the discharge electrodes, produces a strong electric field between the electrodes. The negatively charged particles in the flue gas attract to grounded collector electrode. The collected particles are removed by mechanical vibration. Typical performance 93% removal for fine, and 99.8% for very fine particles does not meet the emission control requirement in some strict areas (countries) like Japan, California.

Electrostatic precipitator

Fabric filter technology of choice on most recently constructed combustion systems. Mechanism Filter bags are connected in parallel in a housing. Particles (>0.1mm) in the gas are trapped on a dust bed on the filter surface. The particles are removed from the filter bags by mechanical shaking, reverse air flow, and pulse-jet. Felted glass, woven glass, and Teflon have been used as fabric filters.

Fabric filter

NOx control Source (food and yard wastes) separation for avoiding fuel NOx Combustion control for avoiding thermal NOx Low excess air operation and staging of combustion First stage; gasification with low-excess air, Second stage; combustion with excess air Flue gas recirculation Flue gas treatment Catalytic reduction Ammonia injection followed by a catalyst bed reaction (metals; copper, iron, chromium, nickel, molybdenum, cobalt, and vanadium). NO + NH3 + 1/4O2  N2 + 3/2H2O (at 275 – 425 oC) up to 90% removal for coal- and oil- burning applications

Acid gases control Source separation of chlorine and sulfur containing wastes Wet scrubbing of flue gases liquid solutions are used to scrub and neutralize Ca(OH)2 or NaOH solution added in venturi scrubber Cooling before wetting and re-heating after wetting Dry scrubbing neutralizing slurries are injected Na2CO3 or Ca(OH)2 added just before the baghouse

Dioxins, furans (DXNs) and metals control Source separation is difficult for DXNs reduction, however, is working properly for metals reduction Combustion control is the principal reducing strategy for DXNs Minimum temperature in thermal system of 900-1070 oC with a minimum residence time of 1 sec Minimization CO emission also minimize DXNs Particulate control is also important for DXNs and metals DXNs and most metals except mercury tend to condense on flyash particles <250oC and can be removed by filters Temp of flue gas must not be kept around 300 oC (avoid De-novo)

Flow diagram of gas treatment Dry scrubbing (Acid gas) Boiler <850Co <2 sec Lime AC Re-heater AC Baghouse PM removal Na(OH) Cooler Re-heater Cooling tower Avoid De-novo Baghouse protect NH3 Wet scrubbing (Acid gas) Incinerator Combustion control NOx catalytic reduction

Ash management Solid residuals Bottom ash Fly ash Scrubber product Bottom ash, fly ash and scrubber product Bottom ash contains considerable amount of metals and glass as well as unburned organics. Amount of unburned organic material in the ash is a measure of performance. (Ash Burnout Index, ABI) sometimes used as a construction material Fly ash particulates removed from the flue gases contains trace pollutants with fine particles, so careful handling is necessary. Scrubber product sludge produced by a wet scrubber

Ash management Heavy metals and trace organics, e.g. DXNs Leaching potential in a landfill EP toxicity test, Toxicity Characteristic Leaching Procedure (TCLP) test Recommended ash-handling Handling; Ash should be properly wetted or covered. Transport; Ash should be covered and leak-resistant. Disposal of flyash only; Disposal should be in a monofill (ash only) equipped with double liners and a leachate collection system. Combined or bottom ash only; Disposal should be in a monofill equipped with a composite or clay liner, or by codisposal in an MSW landfill equipped with a double liner.

Wastewater Wastewater discharges cooling and wash water from wet ash removal systems wet scrubber effluents wastewater from sealing, flushing and housekeeping wastewater from boiler feedwater production cooling tower blowdown Quantities of wastewater produced are relatively minor, but may require pretreatment before discharge into a sewer system

Energy recovery systems Recovered energy electricity steam (heat) using industrial processes or building heating Principal components boilers for steam production steam or gas turbines and reciprocating engines as prime movers for mechanical energy electric generator Cogeneration systems both thermal and electricity production

Energy recovery systems Efficiency of electricity production Average: 10% (overall efficiency, Japan, 2000) many efforts to improve it bigger facilities improve electricity generation system combined turbine RDF use more heat

Disposal method in Asia

Electricity production in major developed countries Total capacity of electricity production by SW incineration (MW) Number of SW incineration plants which produce electricity US UK Germany France Sweden Switzerland The Netherlands Japan 2,820 230 1,000 160 100 180 1,058 102 11 50 90 3 30 5 210 Source: http://www.nedo.go.jp/nedata/14fy/04/b/0004b018

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