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Flue Gas Recirculation and Enhanced Performance of Waste Incinerators under Waste Uncertainty Christos Aristeides Tsiliyannis* ANION Environmental Ltd., 26 Lykoudi Street, Athens Greece ABSTRACT: Variations in waste quantities and composition affect incinerator operating conditions and performance. Fluegas volumes consititute a dominant environmental and financial consideration for efficient waste incinerator (WI) operation, since they affect the temperature, throughput, air pollution control system (APCS) residence time, and pollutant emissions, when the charging rate or composition of any waste is varying. Fluegas recirculation (FGR) in WI is an effective technique for reducing WI atmospheric pollution, mainly NOx emissions, albeit affecting WI throughput, temperature and destruction/removal efficiency. FGR refers to mass recirculation of a possibly cooled fraction of fluegases and differs substantially from fluegas heat recovery. The present work shows that, besides emission control, suitable manipulation of FGR enhances WI performance under waste uncertainty, enabling higher throughput, at the desired temperature and within the allowed APCS residence time range. A dimensionless parameter related to the uncertain wastes’ net enthalpy contribution is isolated, which encompasses heat of reaction and enthalpy outflows from fluegas and solids and which reveals whether throughput is decreasing or increasing with temperature and FGR ratio. Normalized throughput and total fluegas volume isotherms manifest the interdependence and enable manipulation for enhanced environmental and economic performance. chamber fluegases,.19,27 Due to enthalpy loss in the recirculation duct, FGR essentially cools down the incinerator somewhat and is associated with possible robustness problems.5 Being a mass recycle, FGR is fundmanetally different that heat integration (exchange of the heat of flue gases with the feed, air or wastes); the latter redirects enthalpy to the WI and raises its temperature, whereas oxygen concentration in both the primary and secondary air is not affected (21% vol). The present work aims at assessing the impact of FGR on the performance of WI, as reflected by throughput and off-gas volume and emissions and to provide appropriate operator manipulations via the FGR and the temperature of the recirculated flue gas for performance enhancement. It will also attempt to unveil the robustness issues as related to the manipulated parameters. Heat recycle/recuperation is not included. Compliance is presumed if inefficiencies are averted, that is, by maintaining temperature and residence time in the combustor at the desired level guaranteeing acceptable destruction and removal efficiency and also by maintaining fairly constant residence time in the air pollution control systems (APCS).7,18,29

1. INTRODUCTION Throughput, being a key profit factor for waste incinerators, (WI),2,5,9,10,24 is severely affected by increasing uncertainty in quantities and composition of feedstock (wastes). Several wastes may produce high volumes of fluegases, for example, biological sludge (BIS), or large quantities of ash,for example, PCBcontaminated soil. The enthalpy balance necessitates lower overall throughput, if the temperature is to be maintained, since the enthalpy leaving the WI with the fluegases (or the ash) increases. Uncertainty, an area of intense research effort, is associated with plant design,6 supply chains,15,32,33 and demand.25 WI under waste uncertainty must comply with environmental standards.8,12−14,23 Pollutant emissions, which span several orders of magnitude,16 are favored by incomplete combustion (around 600 °C) by fuel-oxidant mixing inefficiency and low combustion residence times.21 Pollutant concentrations and emission rates of principal organic hazardous constituents and heavy metals are affected by feedstock uncertainty, with higher pollutant concentrations in downwind receptors under higher offgas volumes.30 Several techniques are being implemented for improving the performance of WI. Flue gas recirculation (FGR)3,20,35 (or exhaust (EGR)11,17 in internal combustion) emerges as most promising for reducing WI atmospheric pollution, mainly NOx and volatile metal emissions,1,4,19 by resulting in lower total offgas. In practice, whereas a portion of flue gas is recycled back to the incinerator, the secondary combustion air is manipulated by measuring the oxygen conentration of the incineration © 2013 American Chemical Society

Received: Revised: Accepted: Published: 8051

February 19, 2013 June 19, 2013 June 19, 2013 June 19, 2013 dx.doi.org/10.1021/es4007788 | Environ. Sci. Technol. 2013, 47, 8051−8061

Environmental Science & Technology

Article

2. METHOD DESCRIPTION 2.1. Direct Operation: Combustion Mass Balance. In a WI a mixture of wastes is combusted to fluegases and ash, at temperatures 1000−1200 °C. Ash is conveyed for special treatment and disposal. The overall mass balance, eq 1, is combined with combustion reaction 2

Based on the novel linear operator formulation of combustion stoichiometry,34 the fluegas flow rate vector mfg is also a linear expression in f: m̲ fg = ΜSA−1Wf̲

where MSA W is a mxn matrix, invariant if the n waste feedstock types remain the same. Smxp a mxp constant matrix independent of the feedstock.34 The element Sij is the factor multiplying xj in the stoichiometric coefficient of fluegas species i. Under constant excess air, E, and air humidity, h, the matrix S remains constant independent of the waste type or feedrates. Then, the mxp matrix MSA−1 is the combustion process stoichiometric invariant independent of the wastefuel. From eq 4 the total fluegas mass flow rate is

waste feed stock + air = flue gas + bottom ash + fly ash (1) Cx1H x2Ox3Sx4 Cl x5Nx 6Px7Brx8Fx 9 + (1 + Ε)(x1 + φ + x4 + 5/4x 7 − 0.5x3)Ο2 + h(1 + Ε)(x1 + φ + x4 + 5/4x 7 − 0.5x3)100 /21H 2O + (1 + Ε)79/21(x1 + φ + x4 + 5/4x 7 − 0.5x3)N2 → x1CO2 + (2φ + h(1 + Ε)(x1 + φ + x4 + 5/4x 7 − 0.5x3)100

mfg = eT̲ m̲ fg = eT̲ MSA−1Wf̲

/21)H 2O + Ε(x1 + φ + x4 + 5/4x 7 − 0.5x3)O2 + (0.5x 6 + (1 + Ε)79/21(x1 + φ + x4 + 5/4x 7 − 0.5x3))N2 + x4SO2 + x 5ΗCl + 1/2x 7P2O5 + x 8ΗBr + x 9ΗF

(5)

The m-vector of individual fluegas volumetric flow rates is given by Qfg = υ M−1MSA−1W f, or

(2)

to give the fluegases. From stoichiometry: • φ = 1/4 (x2 − x5 − x8 -x9) if x2 > x5 + x8 + x9 • φ = 0 if x2 ≤ x5 + x8 + x9 • h = air humidity (molal fraction) • E = excess air. Oxygen enrichment, say by ζ%, may be included in eq 2 by modifying the nitrogen to oxygen ratio to (79-ζ)/(21+ζ). Other gases such as NOx, volatile metals and organic compounds are also present in the flue gases, while metals may be found in the ash as salts and oxides. Although important as emissions their impact on the mass and enthalpy balance is negligible, being 3 orders of magnitude less than the fluegas flow.26,31 In fact FGR results in considerable reduction of NOx releases.1,4,19,27 Let f =vector of waste flow rates, σi = %ww of noncombustible solids in the ith waste. Assuming negligible mass of non− combustible volatiles, the total ash in eq 1 is given by the linear in f expression bottom ash + fly ash = σ̲ T f ̲

(4)

−1

Q̲ fg = υSA−1Wf̲

(6)

where υ = RT/P is the specific molar volume (=22.4 lt under normal conditions). From eqs 5 and 6, the total mass and volumetric flow rates are obtained by adding the components of the vectors mfg and Qfg, or, as the inner product of mfg or Qfg with the vector e, Q fg = eT̲ Q̲ fg = υ eT̲ SA−1Wf̲

(7)

2.2. Mass Balance Under Flue Gas Recirculation. 2.2.1. Internal and External Flows. In contrast to energy integration via fluegas heat recycle (recovery of a fraction of the fluegas enthalpy in the recuperator), in plants with FGR, the fluegases are redirected to the incineration chamber. Let a fraction η, 0≤ η≤ 1 of the fluegases be directed to the downstream APCS2, whereas a fraction 1−η be recirculated, Figure 1, after passing through the APCS1 (acid control by coke addition, 20) and, possibly, through a temperature regulating heat exchanger (cooler).11,17 FGR features the characteristic of all

(3)

Figure 1. Mass balance of waste incinerators featuring flue gas recirculation, FGR: Steady state massflows, (Gas (blue) and solids (black). Waste feedrate vector = f = ( f1, f 2,..., f n). FGR ratio =1−η. If the quantity or composition of any waste is changed, then the FGR ratio, 1−η, or the FGR temperature, TFGR, can be manipulated in order to avert throughput losses, while maintaining temperature at the desired range and satisfying thermal rating and blower capacity constraints. 8052

dx.doi.org/10.1021/es4007788 | Environ. Sci. Technol. 2013, 47, 8051−8061


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recycle flows: the input and output flows are not modified, but the internal flows multiply as recirculation intensifies. WI FGR flow: η−1 MSA−1Wf̲

(8)

WI output fluegas flow: m̲ fg = MSA−1Wf̲

(9)

Table 1. WI Mass Flows under FGR

Equations 4 and 9 giving the massflow rates of the fluegas components are the same. How is it then possible for FGR to lead to lower flugas volumes,19 which may reach 35%?20 The explanation is that, due to enthalpy loss in the recirculation, FGR essentially cools down the incinerator. This cooling necessitates a lower excess air, compared to direct incineration, in order for the incinerator to operate at the same temperature. As a result, the total volume of fluegases is lower under FGR, when incinerating the same type and amount of wastes at the same temperature. The excess air is included in the matrix S and thus, a structural change is introduced to the stoichiometric invariant MSA−1 under FGR; the invariant is different compared to direct operation or operation under heat recycle (recuperation). What happens if the quantities or composition of certain wastes vary? Can the operator manipulate the FGR ratio or the cooler temperature in order to maintain performance? The linear representation yields the necessary manipulation which maintains the WI/FGR high performance: high throughput with the benefits of low fluegas volumes and low emissions. 2.2.2. Offgas and Solids Outflows. Performance is constrained by process capacity constraints. The offgas and solids’ flows from APCS2 (spray dryer or wet- dry lime injection) are somewhat increased due to the neutralizing lime injection and the carrying agent (air or water). If the APCS2 is a dry/dry system, the auxiliary air, ma, set by the operator at a fraction, ψ, of the total flue gas mass flow rate, ma = ψ mfg, conveys the pulverized lime to the fluegases. In wet/dry designs water conveys the injected lime and the injected waterflow is mw = w mfg. From eq 5,

ma = ψ e̲ Τ MSA−1Wf̲ Τ

−1

m w = w e̲ MSA Wf̲

FGR cooler in FGR cooler out combustor fuegases out solids to wet mechanical treatment solids out

(13)

Q fg = υ( ρ̲ Τ S Α−1W ) f̲

(14)

Ts Tfeed in T TFGR T T

c + σT f + l =(cT + σT+ l T) f = (c + σ+ l) T f η−1 MSA−1W f MSA−1W f

volumetric flow rate, m3/Y (At STP, υ =22 400 if f i in TPY)

stream

Ta out ≈T T Tg out Tgw out

air in (oxygen, nitrogen) oxygen in nitrogen in combustor overall feed combustor air + FG in combustor gases out combustor total outflow fluegases to APCS1 FGR cooler, fluegases in FGR cooler, fluegases out solids out fluegases to APCS2 APCS2 offgases, to the atmosphere, dry-dry system APCS2 offgases to the atmosphere, dry-wet system

Equations 2−14 give the main gas flows as linear expressions of the feedrate vector, f. Coke addition depends on the acid producing potential of the wastes, that is, c = cTf. The solids’ mass flow rate (bottom and fly ash, as well as coke added for acid control in APCS1) equals (cT+σT)f +l. Tables 1 and 2 give the expressions for the various internal and external flows of the WI including individual fluegas constituents’ flow rates; the volumetric flow rate through APCS1 is proportional to η−1, whereas the volumetric flow rate through APCS2 proportional to η−1(1−η). Both are decreasing hyperbolic functions of η in (0, 1] but η−1(1−η) decreases faster than η−1. 2.2. Enthalpy Balance Under FGR. From the mass balance, the recirculated fluegas equals η−1(1−η)MSA−1Wf and the offgas

temperature

(dw−1)T f = (d1−1, d2−1,..., dn−1) (f1, f 2,..., f n)T υ Mair−1 a (eTMSA−1W - eT+ σT) f

wastefeed

The total gas mass and volumetric flow rates to the furnace APCS, mfg, Qfg, are

mfg = (1 + ψ + w) e̲ Τ MSA−1Wf̲

Ts

Table 2. WI Volumetric Flow rates under FGR

(11)

(12)

temperature

f = ( f1, f 2,..., f n) f1+f 2+...+f n = eT f M Mair−1 a (eTMSA−1W − eT+ σT) f f + M Mair−1 a (eTMSA−1W- eT+ σT) f + η−1 (1−η) MSA−1W f −1 η (1−η) MSA−1W f η−1 (1−η) MSA−1W f MSA−1W f + η−1 (1−η) MSA−1W f = η−1 MSA−1W f c + σT f = (cT + σT) f

fluegases to APCS1 fluegases to APCS2 ≈ Offgases offgases to the atmosphere M (I+ψ Mair−1 a eT M) SA−1W f dry-dry system offgases to the atmosphere M (I+ψ Mair−1 a eT M+ dry-wet system w Mw−1 u2 eTM) SA−1W f

(10)

mfg = (1 + ψ ) e̲ Τ MSA−1Wf̲

flow, TPY

stream wastefeed throughput air combustor feed

= u2T υ Mair−1 a (eTMSA−1W − eT+ σT) f = 2nd component of the vector υ Mair−1 a (eTMSA−1W − eT + σT) f u3T υ Mair−1 a (eTMSA−1W- eT+ σT) f = 3rd component of the vector υ Mair−1 a (eTMSA−1W- eT+ σT) f (dw−1)T f + υ Mair−1 a (eTMSA−1W − eT + σT) f + υ η−1 (1−η) SA−1W f υ Mair−1 a (eTMSA−1W − eT + σT) f + υ η−1 (1−η) SA−1W f υSA−1W f + υ η−1 (1−η) SA−1W f = υ η−1 SA−1W f υ η−1 (1−η) SA−1W f + dash−1 σT f

Ts Ts Ts Ts

T T

υ η−1 SA−1W f υ η−1 (1−η) SA−1W f

≈T T

υ η−1 (1−η) SA−1W f

TFGR

dash−1 (σT f + l) υ SA−1W f υ (I+ψ Mair−1 a eT M) SA−1W f

Ta out T Tg out

υ (I+ψ Mair−1 a eT M+ w Mw−1 u2 eT M) SA−1W f

Tgwout

equals MSA−1W f. The outflow of solids cooled to ambient temperature is equal to σT f. The enthalpy balance is (Appendix): ΔΗ total = 0 ⇔ λ̲ T f̲ = kA(T − Ts) + (Tr − Ts) c̲ pf T f̲ + c pash(T − Tr) σ̲ Τ f̲ + (T − Tr) c̲ pT MSA−1Wf̲ + η−1(1 − η)(Τ − ΤFGR ) c̲ pT MSA−1Wf̲ + (Tr − Ts)c pair[ e̲ Τ MSA−1W − eT̲ + σ Τ] f̲ (15) 8053



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Secondary combustion air volumetric flow for diluted oxygen at δ% vol:

Based on the linear mass balance representation, eqs 3−9, the enthalpy balance, eq 15, is also linear in f. It may be solved for the throughput, r, which appears in the last term of eq 15: T

r = e̲ f̲

Vsair = (21 − δ)−1η−1(1 − η)v( eT̲ − 32−1 u̲ 3T )MSA−1Wf̲ (23)

(16)

Primary air flow:

to give

Vpair = total air − Vsair

r = [c pair(Tr − Ts)]−1 kA(T − Ts) + ω̲ Τ f̲ = ωο + ω̲ Τ f̲

= vMair −1( eT̲ MSA−1W − eT̲ + σ̲ Τ) f̲ − Vsair

(17)

(24)

The scalar, ω0 (in TPY) is ω0 = [c pair(Tr − Ts)]−1 kA(T − Ts)

3. RESULTS AND DISCUSSION 3.1. Impact of Uncertainty in Waste Quantities on HWI Throughput and Fluegas Flow Rate. If the waste types are known but the flow rates are uncertain, then only the flows, f i, are varying, and MSA−1W remains invariant, independently of the relative composition of the waste mixture. Thus, charging rate uncertainty is represented by variation in f. If the temperature, T, the fluegas recirculation ratio, η and the FGR temperature, TFGR, are given, eq 23 gives the allowed charging rate for any particular uncertain waste feeding rate, f i: Say the uncertain waste is the nth waste, then

(18)

and the (dimensionless) vector, ω, is ω̲ T = [c pair(Tr − Ts)]−1 {−λT + (Tr − Ts) c̲ pf T + (T − Tr)c pash σ̲ T + η−1(1 − η)(T − TFGR ) c̲ pT MSA−1W + (T − Tr) c̲ pT MSA−1W + (Tr − Ts)c pair(eT MSA−1W + σ̲ T )}

(19)

Comparing to direct operation, the impact of the FGR is included in the FGR enthalpy loss term + η−1 (1−η) (T−TFGR) cpT MSA−1 W, which does not appear in the corresponding enthalpy balance under direct operation. Comparing to heat recycle (recuperator temperature, TR), at the same fraction, η, the enthalpy loss term of the heat recycled fluegas is (1−η) (T−TR) cpT MSA−1 W and the output fluegas enthalpy loss term is η (T−T) cpT MSA−1 W. Hence, under FGR, not only is the required excess air lower for attaining the same temperature with the same feedstock, but the enthalpy balance is different as well. Equation 15 may be solved for the WI temperature, T,

n−1

fn = (1 − ωn)−1(∑ fi (ωi − 1) − ω0) ≥ 0 i=1

where 1 − ωn = 1 − [c pair(Tr − Ts)]−1 {−λn + c pfn(Tr − Ts) + c pashσn(T − Tr) + c̲ pT MSA−1Wn(T − Τr) + (1 − η)η−1 c̲ pT MSA−1Wn(T − T FGR )

T = {kA + [c pash σ̲ T + c̲ pT MSA−1W + η−1(1 − η) c̲ pT MSA−1W ] f̲ }−1 ×{kATs + [λ T − c̲ pf T(Tr − Ts) + c pash σ̲ TTr + c̲ pT MSA−1W Τr

+ c pair[eT MSA−1Wn + σn](Tr − Ts)}

+ c̲ pT MSA−1Wη−1(1 − η)TFGR − c pair(eT MSA−1W − eT̲ + σ̲ T ) ×(Tr − Ts)] f̲ }

(20)

(21)

that is, the vectors [ω1 − 1, ω2 − 1, ···, ωn − 1, ω0] and [f1, f 2, ···, f n, 1] be perpendicular. Condition 21 together with eq 16 consitute necessary and sufficient conditions determining WI operation, temperature, throughput level, fluegas volume, residence time, and performance. In practice, mixing of the FG with the secondary combustion air in the air preheater is regulated so that the diluted air is at oxygen δ = 15%vol to δ = 21% vol and temperature around 621− 900 °C.27 If the overall excess air, E, is to remain constant under FGR operation, then the primary air is regulated accordingly. If the offgas oxygen concentration is targeted at γ% (γ = 6.8%vol in19). The regulating relations are explicitly expressed in our compact form: Excess air for offgas oxygen concentration γ% vol: u̲ 3T MSA−1Wf̲ eT̲ SA−1Wf̲

(26)

The dimensionless parameter (1−ωn) emerges as a key to WI performance. For values of T, TFGR and η where ωn > 1 or ωn < 1, eq 25 gives the charging rate of the uncertain waste, f i, which maintains the WI temperature at T. At the values of T, TFGR and η where 1−ωn = 0 a singularity appears, giving rise to robustness issues: the WI becomes sensitive rendering high performance operation infeasible. As seen from eq 26, wastes with high LHV, (λn) low fluegas flow rate (MSA−1Wn f n) and low quantities of ash, σn f n, correspond to 1−ωn > 0. Putrescible municipal wastes, agroindustrial sludges, biological sludge or PCB/PBB contaminated soil, featuring either too low LHV, or high fluegas flow rates or high inerts’ content, may feature 1−ωn < 0. A similar formulation is possible for direct or heat recycle operation, but the (1−ωn) expressions are different. The offgas volume is set once the flow rate f i is detemined from eq 23 for the corresponding value of η or TFGR via eqs 9 and 14. Evidently, all values of η or TFGR corrrepsonding to the same f n (i.e., same throughput) give the same fluegas volume, provided the overall excess air is fixed, as for instance, via regulation 22−24. 3.2. Impact of Uncertainty in the Composition of Waste on HWI Throughput. If the ultimate analysis of the waste is uncertain, then the column Wn of the matrix W is varying, as well as, the ash content, σn and the LHV, λn. From eqs 3−26, it follows that the impact of the variation in W is passed on to the WI mass/ enthalpy balances via the matrix MSA−1W expressing the flue gas flow rate and the terms which include λn, σn. From matrix multiplication, any variation in the nth column of W, Wn, is only

As a fundamental principle not to be violated, the enthalpy balance allows only those throughput values satisfying eq 15, thereby imposing limitations on the waste flows, f i and consequently on WI income. More specifically, eqs 16 and 17 yield g (ω̲ , f ̲) = : (ω̲ − e̲ )T f ̲ + ω0 = 0

(25)

= 0.32γ (22) 8054



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Table 3. Main Constraints and Flows under FGR maximum mass flow rate of uncertain waste, f n, f n ≤ Cin−1(Li − ∑n−1 j = 1Cij f j) unit 1 2 3 4

thermal rating wastefeed chute, hopper, pump airfeed blower fluegas to APCS1

5 6 7

FGR fan fluegas to APCS2 ≈ offgas offgas to the atmosphere dry-dry system offgas to the atmosphere dry−wet system solids to wet -mechanical treatment

8 9

total mass flow rate, TPY

limit, L

Cin, sensitivity of f n on the constraint

Li =

Values of the scalar Cij, j = 1,2...,n

eT f = eT ( f1, f 2,..., f n) = r eT M Mair−1 a (eTMSA−1W- eT+ σT) f η−1 eTMSA−1W f

qmax Qin max Qair max QAPCS1 max

η−1 (1−η) eTMSA−1W f eT MSA−1W f eTM (I + ψ Mair−1 a eT M) SA−1W f

QAPCS1 max QAPCS2 max QAPCS2 max

i = 1, Clj = λj f n ≤ λn−1 (qmax − ∑n−1 i = 1 λi f i) i = 2, C1j = dj −1 i = 3, C3j = υ [ eT(Mair−1 a (eTMSA−1W − eT+ σT)]j i = 4, C4j = [η−1 υ eT SA−1W]j, f n ≤ C4n−1 (QAPCS1max − ∑n−1 j = 1C4j f j) i = 5, C5j = υ [η−1 (1−η) eTSA−1W]j i = 6, C6j = υ [eT SA−1W]j, f n ≤ C6n−1 (QAPCS2max − ∑n−1 j = 1C6j f j) i = 7, C7j = υ [eTM (I+ψ Mair−1 a eT M) SA−1W ]j

eT M (I+ψ Mair−1 a eT M+ w Mw−1 u2 eTM) SA−1W f (cT + σT) f

QAPCS2 max Qash

i = 8, C8j = υ [eT M (I+ψ Mair−1 a eT M + w Mw−1 u2 eTM) SA−1W ]j i = 9, C9j = dash −1 (cT + σT)j

Figure 2. Case study, Waste mixture 3,4,6: Uncertainty in waste 3 (BIS, λ3 = 2000 kcal/kg). Design conditions: T0 = 1100 °C, nominal throughput, r0 = 8000 TPY, η0 = 0.6. 2a: the parameter 1−ω3 as a function of η in the investigated temperature range 1000−1200 °C. 2b: Normalized throughput variation (r−r0)/r0, or normalized volumetric flow rate variation, (Qfg−Qfg0)/Qfg0 versus FGR temperature, TFGR, at the nominal design FGR ratio, η = η0 = 0.6 (temperature values T = 1000 °C, (T− T0 = −100), T = 1050 °C, (T−T0 = −50), T = 1100 °C, (T−T0 = 0), T = 1050 °C, (T−T0 = 50), T = 1200 °C, (T−T0 = 100) and normalized heat rate, q/qmax, isotherms, versus TFGR. 2c: normalized throughput variation isotherms and normalized heat rate, q/qmax, isotherms, versus FGR ratio, η. At the value of η where q = qmax, that is, q/qmax = 1, the corresponding (r−r0)/r0 isotherm intersects the thermal rating constraint, that is, r = rQmax or (r−r0)/r0 = (rqmax − r0)/r0. (Normalized throughput variation minimum for all graphs: Δr/r0 = (Σn−1 i−1 f i − r0) /r0), uncertain waste = nth waste.

affecting the nth column of MSA−1W, which, multplied by the waste feedrate vector, f, picks-up only the flow rate f n, and thus the impact of qualitative uncertainty on fluegas is reflected by only varying the respective column of W. Hence, only the nth column of the matrix MSA−1W must be modified in eqs 4−14, while in eqs 15−26, the term λn and the terms including σ must also be modified with the new values of λn and σn. The term

involving the heat capacity, cpf, of the uncertain waste will vary somewhat, however this term is relatively small, since it is multiplied by (Tr − Ts) and its variation is negligible. 3.3. Impact of FGR Ratio and Temperature on WI Performance. The following relations (Appendix) express the sensitivity of the WI throughput and fluegas volume with respect to FGR ratio, η, with respect to WI temperature, T and with 8055



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Figure 3. Case study, Waste mixture 3,4,6: Dried BIS, λ3 = 3000 kcal/kg . 3a: the parameter 1−ω3 as a function of η in the investigated temperature range 1000−1200 °C. 3b: Normalized throughput variation (r−r0)/r0, or normalized volumetric flow rate variation, (Qfg−Qfg0)/Qfg0, versus FGR temperature, TFGR, at FGR ratio, η = 0.8 (temperature values T = 1000 °C, (T−T0 = −100), T = 1050 °C, (T−T0 = −50), T = 1100 °C, (T−T0 = 0), T = 1050 °C, (T−T0 = 50), T = 1200 °C, (T−T0 = 100) and normalized heat rate, q/qmax, isotherms, versus TFGR. 3c: normalized throughput and volumetric flow rate variation isotherms and normalized heat rate, q/qmax, isotherms, versus FGR ratio, η at TFGR = 800 °C.

The above show that if 1−ωn > 0, the throughput and fluegas volumetric flow rate decrease with η (i.e., they increase with FGR ratio, 1−η). They both decrease with TFGR and they both increase with temperature. The rates of increase are given by eqs 27−32. Equations 25−32 provide the key to η or TFGR manipulation for optimizing WI performance under waste uncertainty; in addition they manifest the dominant role of the dimensionless parameter (1−ωn) in WI performance: its sign determines the direction of manipulation and its size dominantly affects the necessary gain. 3.4. Capacity Constraints and WI Performance Representation. According to manufacturer’s specifications the WI must operate within its capacity limits including thermal rating of the refractory, induced draft of the APCS fans, feed hopper volumetric capacity, etc. Our formulation allows such constraints to be explicitly expressed in terms of the uncertain waste (Table 3). For instance, for thermal refractory rating: λT f ≤ qmax implying that f n ≤ λn−1(qmax − Σi n−1 = 1 λi f i). The operator may manipulate the fluegas recirculation ratio, η, or the FGR temperature, TFGR, in order to maximize f n and consequently the throughput, at the value dictated by the thermal rating. Since the APCS2 fluegas volume will also be increasing, the corresponding constraint should also be checked (Table 3). Besides being the most important mass capacity constraint, the fluegas volume relates to atmospheric releases and economic considerations. In the presence of waste uncertainty, the normalized

respect to FGR temperature, TFGR. If the nth fuel is uncertain then μ=

∂r ∂η

= − (1 − ωn)−1[c pair(Tr − Ts)]−1 (T − TFGR )η−2[ c̲ pT MSA−1W ]T f̲

(27) ν=

∂r ∂Τ

= (1 − ωn)−1[c pair(Tr − Ts)]−1 {kA + [c pash σ̲ Τ + η−1 c̲ pT MSA−1W ] f̲ }

(28)

ξ=

∂r ∂ΤFGR

= −η−1(1 − ωn)−1[c pair(Tr − Ts)]−1 [ c̲ pT MSA−1Wf̲ ] (29)

∂Q fg ∂η ∂Q fg ∂T ∂Q fg ∂TFGR

= v eT̲ SA−1Wu̲ nμ = v eT̲ SA−1Wu̲ nν = v eT̲ SA−1Wu̲ nξ

(30)

(31)

(32) 8056



Article

Figure 4. Case study, Waste mixture 3, 4, 6, 7, 8, 12, 13, 14: Uncertainty in waste 7. (PCBs and PBBs): (C, H, O, S, N, Cl, P, Br, F; inerts) (23.08, 2.40, 6.44, 0.52, 0.37, 10.00, 0, 6.05, 0.00; 51.13 and LHV 5 000 kcal/kg). 4a: the parameter 1−ω7 as a function of η in the allowed temperature range. 4b: Normalized throughput variation (r−r0)/r0, or normalized volumetric flow rate variation, (Qfg−Qfg0)/Qfg0, versus temperature at η = 0.6. 4c: normalized variation isotherms and normalized heat rate isotherms versus η at TFGR = 800 °C.

fluegas volumetric flow rate variation, for example, for ψ = 0, w = 0, is given by ΔQfg/Qfg0 = eTSA−1W(f − f0)/e TSA−1W f0 The dependence of WI performance on η or TFGR may be represented by the joint plots of Δr/r0 = eT(f − f0)/eTf0, ΔQfg/Qfg0 and q/qmax (see Case Study). The slopes are readily determined from eqs 27−32 (Appendix). Note that ΔQfg/Qfg0≠ Δr/r0 since MSA−1W is not symmetric. 3.5. Enhanced Performance of Waste Incinerator via FGR − Environmental Relevance. If waste quantities or composition vary, the FGR ratio and FGR temperature may be used to enhance WI performance by enabling higher throughput and compliance to emission standards. Fluegas volumes increase, albeit at a lower rate. Performance is not necessarily enhanced by thermal substitution of wastes. Manipulations and related environmental repercussions: 1. Under varying waste feedrates or composition, the throughput, r, and fluegas volume, Qfg, at the design temperature, will vary according to the FGR ratio 1−η and the cooler or FGR temperature, TFGR. Similarly, under the design FGR ratio, the throughput and fluegas volume depend on WI temperature, T and cooler temperature, TFGR. 2. If uncertainty lies with the ith waste, then the throughput r, and the fluegas volume, Qfg are increasing with T, increasing with the FGR ratio (1−η) (or decreasing wιth η) and decreasing with TFGR, if and only if 1−ωi > 0. In this case (1−ωi > 0), if, upon charging the uncertain waste at a varying feeding rate, the temperature drops, the throughput also decreases and a larger feedrate of the uncertain waste is feasible and may restore the temperature

to the desired operational value, T. If the operator reduces η (that is, inceases the FGR ratio) then the throughput may be further increased at the same WI temperature, T, (moving along the WI isotherm). The fluegas volumetric flow rate constraint should be checked, since the fluegas flow rate through APCS2 increases as well; the residence time in APCS2 decreases, resulting in less efficient emission controla trade-off between environmental compliance and throughput (profits) to be balanced. Similarly, if the operator reduces the FGR temperature, TFGR. 3. If uncertainty lies with the ith waste, then the throughput, r and fluegas volume, Qfg, decrease with T, decrease with the FGR ratio (1−η) (or increase wιth η) and increase with TFGR, if and only if 1−ωi < 0. If the temperature drops by charging the ith waste, then in order to maintain the feedrate and maximize the throughput, the operator must either increase η (or decrease the FGR ratio (1−η)) or increase the FGR temperature, TFGR. Increasing the throughput beyond the design value, increases the APCS2 volumetric flow rate and reduces the residence time through the APCS2, resulting in higher offgas pollutant concentrations. Capacity constraints (Table 3) should be checked during all such manipulations. The main ones are (a) thermal rating: It limits the feasible maximum throughput and offgas flow rate, (b) APCS2 blower: The APCS2 blower capacity is attained first, becoming the throughput limiting constaint if the uncertain waste produces high fluegas volumes, for example, biological 8057



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Figure 5. Case study, Waste mixture 3, 4, 6, 7, 8, 12, 13, 14: Uncertainty in waste 13 (SRF). 5a: the parameter 1−ω13 as a function of η. 5b: Normalized throughput variation (r−r0)/r0, or normalized volumetric flow rate variation, (Qfg−Qfg0)/Qfg0, versus FGR temperature, TFGR, at η = 0.6. 5c: normalized variation isotherms and normalized heat rate isotherms versus FGR ratio, η, at TFGR = 800 °C.

depleting fluorocarbons (ODF) from an electrical/electonic waste facility and aliphatic organic solvents (AOS). The WI operability was assessed by the presented method (thermochemical parameter values from refs 2,22,28). Characteristic scenaria presented here: (a) Impact of variations in BIS composition and heating value on WI performance. (b) potential PCB/ PBB coincineration under variation in PCB/PBB or in SRF charging rate. Waste ordering: 1: Coal, 2: tires, 3: BIS, 4: RS, 5: AS (Benzene), 6: AS (Toluene), 7: PCB or PBB, 8: PVC, 9: PP, 10: PE, 11: HDPE, 12: ODF, 13: SRF, 14: AOS. (a) Incineration of RS (4000 TPY) and AS (4000 TPY) at Tc = 800 °C, gives mfg = [125 187, 135 000, 152 127] tonmoles for η = [0.6, 0.72, 1 (direct operation)] at E = [20%, 30%, 47%], γ = [0.0330, 0.0458, 0.0638] and δ = [0.17,0.17,0.17], respectively, corroborating the FGR benefits compared to direct operation. Coincineration of BIS (varying charging rate, LHV3 = 2000 kcal/kg) and isobaric charging of RS, AS: Figure 2 depicts the factor 1−ω3 (eq 26), the joint graph of the normalized throughput and fluegas flow rate variation isotherms (Appendix, eqs A8−A13) with respect to FGR ratio, η and FGR temperature, TFGR (eq 29), the normalized heat rate and the maximum throughput due to thermal capacity constraint. Since 1−ω3 < 0 everywhere, manipulation is robust. In accordance with eqs 25−32 the throughput and APCS2 fluegas flow increase with η, or decreases with FGR ratio, (1−η); they decrease with temperature T and increase with TFGR. Hence, it is maximized on any isotherm

sludge. Since the volumetric flow rate in APCS2 increases with auxiliary air fraction, ψ, or with wet lime injection fraction, w, (Table 2), lowering ψ and/or w decreases the fluegas volume, Qfg, through APCS2. It may therefore compensate for the increase due to higher throughput, at the expense of less efficient acid control and higher emissions. Alternatively, the blower fan must be revamped to higher capacity so as to render the thermal rating as the throughput limiting constraint. (c) APCS1 blower fan: the volumetric flow rate is inversely proportional to η, Table 2. Thus in case (2), which corresponds to 1−ωi < 0 and requires increase of η, (or decrease of the FGR ratio) the APCS1 fluegas volumetric flow rate increase is compensated and the APCS1 will not likely limit the throughput. In contrast, in Case (1) which corresponds to 1−ωi > 0 and requires decrease of η, the APCS1 flow increases and the APCS1 blower may limit the throughput value, if attained first. Similarly, but at faster rate, for (d) FGR blower: the volumetric flow rate through the FGR blower is proportional to η−1(1−η) which decreases faster than η−1 with η.

4. CASE STUDY A hazardous WI with fluegas recirculation, thermal capacity (limiting constraint) of 90 × 106 Mcal/year is planned in the greater Athens area to incinerate at 1150οC a 8 000 TPY mixture of commercial solid wastes, industrial slurries/sludges, plastic from post shredder end-of-life-vehicle facility, solid refuse fuel (SRF) from a nearby muinicipal waste plant, biological sludges (BIS), refinery sludges (RS), spent aromatic solvents (AS), polyhalogenated biphenyls (PCBs and PBBs), ozon 8058



Article

by decreasing FGR or by increasing TFGR until Qfg reaches the maximum allowed value. Other capacity constraints (Table 3) could be readily checked as horizontal lines on the joint graphs. APCS2 residence times are checked via eqs 11, 14 and Table 2. Figure 3 corresponds to dried BIS (LHV3 = 3000 kcal/kg). It is seen that 1−ω3 changes sign in all isotherms implying a larger sensitivity; above the singular point, 1−ω3 > 0 and the manipulations are reversed (see (b) below). (b) Coincineration of isobaric mixture of BIS, RS, AS, PVC, ODF, SRF, AOS, and PCB/PBB at varying charging rate. Figure 4 depicts 1−ω7 (eq 26), the normalized throughput and fluegas flow variation isotherms with respect to η and TFGR, the normalized heat rate and the binding thermal capacity constraint. Operation is robust since 1−ω7 > 0 everywhere. Throughput and APCS2 fluegas flow decrease with η or increase with FGR ratio, (1−η), increase with temperature, T and decrease with TFGR. Hence, performance is enhanced on any isotherm by increasing FGR or by decreasing TFGR, until Qfg reaches the maximum allowed value. Figure 5 corresponds to fixed charging rate of PBB with varying SRF feedrate. At the singular point (1−ω13 = 0) the direction of manipulations is reversed; for 1−ω13 > 0 Figure 5b, c give the appropriate manipulations for performance enhancement: for example, at the design temperature (T = 1150 °C) a lower TFGR (Figure 5b) or a lower FGR ratio (Figure 5c) will allow higher throughput up to the thermal rating constraint, or the APCS2 blower constraint.

Also, μ=

∂ fi ∂f T ∂ω̲ ∂r = = i ∂ω̲ ∂η ∂η ∂η

∂Q fg

∂η

= v eT̲ SA−1Wu̲ i

Normalized variations eT̲ ( f̲ − f0 ) Δr = r0 eT̲ f0

(A8)

∂(Δr /r0) μ ∂(Δr /r0) ξ = , = ∂η r0 ∂TFGR r0

(A9)

ΔQ fg

=

Q fg0

eT̲ SA−1W ( f̲ − f0 ) eT̲ SA−1W f0

∂(ΔQ fg /Q fg0)

−1

∂η

=

v eT̲ SA−1Wu̲ nμ ∂(ΔQ fg /Q fg0) , Q fg0 ∂TFGR

=

v eT̲ SA−1Wu̲ nν Q fg0

−1

+ η (1 − η)(Τ − ΤFGR ) c̲ p MSA Wf̲ + (Tr − Ts)c pairmair

(A1)

But from eq 1,

q qmax

mair = eT MSA−1W f̲ + σ̲ T f̲ − eT̲ f̲ = eT̲ MSA−1W f̲ − eT̲ f̲ + σ̲ T f̲

=

λ̲ Tf qmax

∂(q/qmax )

(A2)

∂η

and substitution in eq A1 gives eq 15. Equations 16−19 are obtained by solving for eT f = r. From eq 19 it follows that:

■

∂ω̲ Τ = −η−2[c pair(Tr − Ts)]−1 [ c̲ pTMSA−1W ](Τ − ΤFGR ) ∂η

=

(A10)

(A11)

(A12)

λT u̲ nμ ∂(q/qmax ) λT u̲ nν = , ∂TFGR qmax qmax

(A13)

AUTHOR INFORMATION

Corresponding Author

*Phone/fax: 0030-210-2285650; e-mail: [email protected].

(A3)

Notes

The authors declare no competing financial interest.

■

Τ

∂ω̲ = [c pair(Tr − Ts)]−1 {c pash σ̲ Τ + η−1 c̲ p TMSA−1W } ∂Τ

NOMENCLATURE Apxp−1 the inverse of the pxp diagonal matrix of atomic weights Apxp ={diag (AW)j} −1, of the chemical elements in the waste fuel mixture C, H, O, S, N, Cl, P, Br, F APCS air pollution control system

(A4)

∂ω̲ Τ = −[c pair(Tr − Ts)]−1 {η−1 c̲ pTMSA−1W } ∂ΤFGR

∂fi T ∂ω̲ ∂ω̲ ∂η

= veT SA−1Wu̲ iμ

+ c pash(T − Tr) σ̲ f̲ + (T − Tr) c̲ p MSA Wf̲ T

∂v eT̲ SA−1Wf̲

=

∂η

ΔΗ total = 0 ⇔ λ̲ T f̲ = kA(T − Ts) + (Tr − Ts) c̲ pf T f̲ −1

(A7)

From eq 21, the implicit function theorem for a scalar function, g, of n+1 variables gives: ((∂f i)/(∂ω))T = −((∂g)/(∂f i))−1 ((∂g)/ (∂ω))T = −(ωi − 1)−1 f T. Equation 25 is obtained directly by substituting in A6, and using A3. Similarly for eqs 26 and 27. Also,

■

T

(A6)

The term ((∂f)/(∂ω)) in eq A6 is the matrix of which the ith row is equal to ((∂f i)/(∂ω)). If uncertainty is associated with the ith waste then

APPENDIX By neglecting the hyperbolic term (six orders-of-magnitude smaller in the ranges of interest, for example, (Tr, T)), the heat capacities are expressed as cp = a + b/2(T + Tr) and consequently the enthalpy balance becomes:

T

⎛ ∂ f̲ ⎞ ⎛ ∂ f̲ ⎞ ∂ω̲ ∂r = eT̲ ⎜ ⎟] = eT̲ ⎜ ⎟ ∂η ⎝ ∂η ⎠ ⎝ ∂ω̲ ⎠ ∂η

(A5) 8059


Environmental Science & Technology a c γ cp cpf cp air δ e f h I LHV mfg mfg Mmxm

Mair Qfg r R Smxp T ui Vpair, Vsair Wpxn

Article

ψ mass fraction of auxiliary air with respect to the furnace flue gas (aux. air is mixed with the flue gases in the lime scrubber) ω0 scalar in the throughput expression, depending only on T, TPY ω robustness vector, dimensionless

= vector giving the oxygen and nitrogen mass flows from total air mass flow in the order of the flue gas vector constituents a T = (0, 0, 0.21, 0.79, 0,....0) = coke added for acid control =cTf offgas oxygen vol concentration vector of heat capacities of the flue gases (cp1 = cpCO2, cp2 = cpH2O, cp3 = cpO2, cp4 = cpN2, cp5 = cpSO2, cp6 = cpHCl, cp7 = cpP2O5, cp8 = cpHBr, cp9 = cpHF in kca/kg °K feed heat capacity vector, in kca/kg °K air heat capacity in kca/kg °K diluted secondary combustion air (by recirculated FG) oxygen vol concentration orthodiagonal vector eT =[1, 1,...,1] = ( f1, f 2,..., f n)T wastefeed mass flow rate vector ( f i in t/year, TPY) air moisture, molal fraction identity matrix lower heating values = λ vector of fluegas mass flow rates = mass flows of (CO2, H2O, O2, N2, SO2, HCl, P2O5, HBr, HF...) total mass of flue gases from reaction 1 driven to the air pollution control system (APCS) = the mxm fluegas products’ molecular weight (MW) diagonal matrix: = diag {MW(CO2), MW(H2O), MW(O2), MW(N2), MW(SO2), MW(HCl) MW(P2O5), MW(HBr) MW(HF) } = diag {44, 18, 32, 28, 64, 36.5, 142,..) = MWair = molecular weight of air = 28.84 WI fluegas’ volumetric flow rates (Nm3/h) throughput, TPY universal gas constant = 0.08206 (atm lt) /(mole K) stoichiometry matrix of wastes converted to fluegas products temperature: T = furnace, Ts = ambient = 25 °C, Tr = reference (heat of reaction)=150 °C for the lower heating value (−ΔHreaction) TFGR = FGR cooler the unit vector in the ith direction, for example, u1T [1, 0,...,0] etc volumetric flow rates of primary and secondary combustion air pxn matrix of net fuel weight composition, without the noncombustibles (slag): the ith column of W is the % weight composition of the ith fuel in the combustible elements, multiplied by the net combustible content (1 − σi) of the ith fuel, Wj = (1 − σi) (% C, %H, %O, %S, %N, %Cl, %P, %Br, %F)T j = 1, 2..., n (p = 9 here)

Superscripts T

transpose of a vector or a matrix

Symbols

■

=: equal by definition

REFERENCES

(1) Agrawal, R. K.; Wood, S. C. Innovative solutions for cost-effective NOx control. Pollut. Eng. 2002, 34 (6), 18−25. (2) ANION Environmental Ltd, 2009, Environmental & Economic Assessment of Waste Treatment, Hellenic Min. of Env. http://www.epper. gr/el/Pages/eLibrary.aspx?SType=1&SearchID=10394003. (3) Brem, G., 2003. Advanced grate furnaces for future waste incineration. ISWA Beacon Conference Waste to Energy: State of the Art andLatest News. Malmö (S). www.iswa.ch/Info/Documents/ WastetoEnergy03/Brem.pdf. (4) Burnley, S. J.; Aplin, P. Controlling oxides of nitrogen emissions from a municipal-waste incinerator by flue-gas recirculation. J. Inst. Energy 1999, 72 (493), 165−169. (5) Castaldi, M. J.; Themelis, N. J. The case for Increasing the global capacity for waste to energy. Waste Biomass Valor 2010, 1, 91−105. (6) Cheng, L.; Subrahmanian, E.; Westerbeg, A. W. Design and planning under un-certainty: Issues on problem formulation and solution. Comput. Chem. Eng. 2003, 27, 781−801. (7) Clark, W. D.; Seeker, W. R. Engineering analysis of hazardous waste incineration energy and mass balance. Nucl. Chem. Waste Manage. 1987, 7 (1), 21−28. (8) CleanAir Act, 1970 and Clean Air Act Amendments, 1977 (9) Consonni, S.; Giugliano, M.; Grosso, M. Alternative strategies for energy recovery from municipal solid waste. Part A: Mass and energy balances. Waste Manage. 2005, 25, 123−135. (10) Consonni, S.; Giugliano, M.; Grosso, M. Alternative strategies for energy recovery from municipal solid waste. Part B: Emission and cost estimates. Waste Manage. 2005, 25, 137−148. (11) Detroit Diesel Corporation: The ABC’s of Exhaust Gas Recirculation. Detroit Diesel Corporation, Detroit, MI, 2003. http:/ www.detroitdiesel.com/public/brochures/6SA591.pdf. (12) Directive 2000/76/EC of the European Parliament and of the Council of 4 December 2000 on the incineration of waste, OJ L 332, 28.12.2000, p. 91−111. (13) Directive 2001/81/EC, on maximum emission limits for atmospheric pollutants. (14) Federal Water Quality Act, 1965 (USA) (15) Gaustad, G.; Li, P.; Kirchain, R. Modeling Methods for Managing Raw Material Compositional Uncertainty in Alloy Production. Resour. Conserv. Recycl. 2007, 52 (2), 180−207. (16) Hinshaw, G. D.; Trenholm, A. R. Hazardous waste incineration emissions in perspective. Waste Manage. 2001, 21 (5), 471−475. (17) Kopa, R. D. and Kimura, H. Exhaust gas recirculation as a method of nitrogen oxides control in an internal combustion engine. In Proceedings of the APCA 53rd Annual Meeting, Cincinnati, OH,1960. (18) LaGrega, M. D., Buckingham, P. L. and Evans, J.C., The Environmental Resources Management Group, Hazardous Waste Management; Mc Graw Hill: New York, 1994; ISBN 0-07-113454-9. (19) Liuzzo, G., Verdone, N., Bravi,M. The benefits of flue gas recirculation in waste incineration. Waste Manage., 2007, 27 (1), 106− 116. (20) Martin GmbH, www.martingmbh.de. (21) Mascolo, G.; Spinosa, L.; Lotito, V.; Mininni, G.; Bagnuolo, G. Lab-scale evaluations on formation of products of incomplete combustion in hazardous waste incineration: Influence of process variables. Water Sci. Technol. 1997, 36 (11), 219−226.

Greek

ΔH = enthalpy with respect to a reference level η axhaust gas recirculation fraction, that is, directed back to the combustion chamber λ vector of lower heating values of the wastes, 1,2,...,n, that is, λT f = total annual HWI thermal load μ sensitivity of throughput with respect to η ν sensitivity of throughput with respect to T ξ = sensitivity of throughput with respect to TFGR ρ = [I + (Mair−1ψ+Mw−1w)M] e, that is, component ρi = [1+ψ(MWi/MWair) + w(MWi/MWwater)]] σ = (σ1, σ2,..., σn)T = vector of inerts’ content, σi = %ww of noncombustible solids in the ith waste υ specific molal flue gas volume under pressure P and temperature T conditions = RT/P 8060



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(22) Perry, H. R., Chilton, H.C. Chemical Engineers Handbook; Mc Graw Hill: New York, 1973. (23) Resource Conservation and Recovery (RCRA) Act, 1976), and RCRA Regulation for Hazardous Waste Incinerators, 1980 and RCRA Amendments, 1985. (24) Santoleri, J., Theodore, L., Reynolds, J. Introduction to Hazardous Waste Incineration, 2nd ed.; Wiley-Interscience: New York, 2000; ISBN 0471017906, 9780471017905. (25) Schwartz, J. D.; Wang, W.; Rivera, D. E. Simulation-based optimization of process control policies for inventory management in supply chains. Automatica 2006, 42, 1311−1320. (26) Seinfeld, H. J. Atmospheric Chemistry and Physics of Air Pollution; John Wiley & Sons: New York, 1986 (27) Suvarnakuta, P.; Patumsawad, S.; Kerdsuwan, S. Experimental study on preheated air and flue gas recirculation in solid waste incineration. Energy Sources, Part A, 2010, 32 (14), 1362−1377. (28) Theodore, L. and Reynolds, J. Introduction to Hazardous Waste Incineration; Wiley Interscience: New York, 1987. (29) Theodore, L.; Reynolds, J. Incineration of Hazardous Wastes; Wiley Interscience: New York, 1989. (30) Travis, C. C.; Holton, G. A.; Etnier, E. L.; Cook, S. C.; O’Donnel, F. R.; Hetrick, D. M.; Dixon, E. Potential health risk of hazardous waste incineration. J. Hazard Mater. 1987, 14 (3), 309−320. (31) Tsiliyannis, C. A. Comparison of environmental impacts from solid waste treatment and disposal facilities. Waste Manage. Res. 1999, 17, 231−241. (32) Tsiliyannis, C. A. End-of-life flows of multiple cycle consumer products. Waste Manage. 2011, 31, 2302−2318. (33) Tsiliyannis, C. A. Internal Cycle modeling and environmental assessment of multiple cycle consumer products. Waste Manage. 2012, 32, 177−193. (34) Tsiliyannis, C. A. Alternative fuels in cement manufacturing: Modeling for process optimization under direct and compound operation. Fuel 2012, 99, 20−39. (35) Urban, A. I. Optimization of combustion by recirculation of fluegas. In Recycling International, 1982; pp. 259−264.

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