Wai-Fah Chen.The Civil Engineering Handbook

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Incinerators 13-17

Abrasion is the simplest mechanism; it forms particulate by the straightforward action of the solid

mass rubbing against itself and against the walls of the combustion chamber. Since abrasion tends to

form coarse particulate that can be readily removed by a reasonably well-designed APCD, it is not usually

of primary concern when evaluating combustors, and it will not be discussed further.

The formation of particulate by ash formation occurs when ash-containing liquid wastes and fuels are

burned, the organics are destroyed, and the inorganic ash remains behind. The size of the resulting particulate

is a function of the concentration of the inorganic materials in the fuel, the size of the droplets formed by

the nozzle, and of the ash’s physical characteristics. When a droplet of atomized liquid leaves the nozzle and

hits the combustion chamber, the organic portions vaporize and burn leaving the ash behind in suspension.

Depending on the composition of the ash, a fraction may volatilize as well (Barton, 1988). Regardless of

whether this occurs or not, nearly the entire inorganic fraction is typically entrained by the gas ﬂow.

The particulate formed by volatilization/condensation is especially germane to the emission of metals

(EPA, 1989c, 1991, 1992, 2001). Many metals and their salts will form vapors at the temperatures of the

ﬂame and the postﬂame zones of a combustion chamber. When the vapors cool, they condense to form

very ﬁne (<1 micron in diameter) particulate, which tends to be relatively difﬁcult to capture in an air

pollution control device. Volatilization of metals and other inorganics can occur whether the waste or

fuel is a solid or a liquid. As long as it contains an inorganic fraction, it may volatilize. This phenomenon

is of especial concern when the inorganic fraction includes toxic metals (i.e., Cr, Cd) or their compounds.

The size of the entrained particles can range from 1 µm to over 50 µm, but typically does not exceed

20 µm in diameter (Petersen, 1984; Goldstein and Siegmund, 1976). The particle size distribution can

signiﬁcantly affect the collection efﬁciency of air pollution control systems and the ability to meet RCRA

particulate standards. Generally, particles less than 1 micron in diameter are more difﬁcult to collect,

requiring higher energy wet or dry control devices.

Another source of ﬂue gas entrained particulate is the dissolved salts in quench water and sometimes

the scrubber. Particulate forms in the quench when the water is evaporated by the hot ﬂue gases. The

solids dissolved and suspended in the water could form particulate. Particulate formation in the scrubber

is less common but can occur if the quench does not cool the ﬂue gas completely or if gas velocities in

the scrubber are high enough to entrain liquid droplets. The salts, such as NaC1, can escape to the ﬂue

gas along with entrained mist. Although mist elimination equipment provides an added measure of

control, some of the salts can escape to the stack and will eventually be measured as particulate by

conventional sampling methods. The contribution of these salts to the overall particulate loading, while

not large, could result in the failure to meet the particulate emission limits.

A model to predict the partitioning of toxic metals was developed but found to be of limited usefulness

(Barton et al., 1988). Toxic metal emissions from hazardous waste incinerators can result from the

following mechanisms:

•Mercury, a volatile metal, is almost completely emitted from the stack.

•Less volatile metals, such as antimony (Sb), lead (Pb) and cadmium (Cd), vaporize and enter the

gas stream. The higher the incinerator temperature, the higher the vaporization rate. As the gas

cools, the vapors condense homogeneously to form new, less than one micron particles and

heterogeneously on the surface of entrained ash particles, preferentially to ﬁne particulate, because

of their large surface area.

•Under combustion conditions, metals react to form compounds like chlorides and sulﬁdes.

Because these compounds (especially many metal chlorides) are often more volatile than the

original metal species, they more readily vaporize and enter the gas stream. Upon secondary

oxidative reactions, these metals can return to their original form and will proceed to condense

into new or existing particles as mentioned above

•Metals and their reactive species can also remain trapped in the ash bed of solid waste incinerators

contributing the metal loading of the residual ash. Entrainment of particulate from the ash bed

into the gas stream can, however, contribute to the ﬂue gas loading of toxic metals.

13-18 The Civil Engineering Handbook, Second Edition

Material and Energy Balances

Stoichiometry and thermochemistry form the basis for most design calculations for incinerators and, in

fact, all combustors. One of the simplest forms of combustion is that of charcoal or coke which may, for

the purpose of this calculation, be assumed to be pure carbon. The major chemical reaction is as follows:

(13.4)

One molecule or mole of carbon (12 g or lb depending on the units chosen) combines with one

molecule or mole of oxygen gas (32 g or lb) to form one molecule or mole of CO

(44 g or lb) gas. If

the source of oxygen for the combustion is air (approximately 21 mole or volume percent oxygen and

79 mole or volume percent nitrogen), then the 1 mole of oxygen brings with it 79/21:3.76 moles or 105 g

or lb of nitrogen. Note that for combustion calculations, the other components of air (except for possibly

the water vapor) are usually ignored. The calculations in the following example are performed using

English Units. If metric units are to be used, the volume of one gram-mole of gas at STP, 22.4L, can be

used in place of 387 lb-mole/scf.

By the ideal gas law, 1 lb-mole of any gas at STP occupies 387 ft

the combustion of 12 lb of carbon

will produce 387 scf of CO

and will consume 387 scf of oxygen gas. If air is used as the source of oxygen,

1456 scf of nitrogen gas will be moved through the system.

The amount of oxygen or air required to exactly burn all of the fuel available is called the “stoichiometric

oxygen,” “stoichiometric air,” “theoretical oxygen,” or “theoretical air.” Virtually all combustion devices

operate with an excess of combustion air, i.e., at over 100% theoretical air with the amount fed speciﬁed

by the “equivalence ratio, ER” deﬁned by:

(13.5)

An alternative method of specifying the amount of air actually fed to the combustor is the “percent

excess air,” which is deﬁned by:

(13.6)

If the combustion of carbon were performed using 120% excess air, ER = 2.2, then the same amount

of carbon and CO

would be involved, but the combustor would be fed 2.2 times the theoretical amount

of air than under stoichiometric conditions. Hence, 2.2 lb-moles or 851 scf of oxygen and 8.27 lb-moles

(3203 scf) of nitrogen would pass through the system. The mass and volumetric ﬂow rates of the

combustion air and ﬂue gas streams can, thus, be computed by using stoichiometry and the concept of

excess air. The same calculations can be applied to complex systems.

The percent excess air (also called excess oxygen) can be readily calculated for an actual combustor

from the analysis of oxygen and carbon dioxide in the combustion gases. Such a determination is typically

performed using an Orsat apparatus or oxygen monitor and the following equation:

(13.7)

Equation (13.7) assumes that both the amount of nitrogen in the wastes and fuel and the CO in the

ﬂue gas are negligible. Both assumptions are usually acceptable for incinerator applications. The value

0.266 in Eq. (13.7) is simply the quotient 21/79, the ratio of oxygen to nitrogen in air. This equation can

be used along with a mass balance and energy balance to cross-check the ﬂue gas ﬂow rate, composition,

CO CO+Æ

volume of combustion air

volume of theoretical air required

()

Percent Excess Air %EA ER==-

()

*1 100%

%EA

0 266.

Incinerators 13-19

and temperature against the feed rate, composition, and heating value of the wastes and fuels fed to the

incinerator to determine whether the measurements performed are mutually consistent.

Mass balances on more complex systems are performed in the same way. No matter how complex the

system, the calculations can be based on the elemental feed rates of the streams. Consider the combustion

of a mixture of methane and carbon tetrachloride in air. The balanced chemical reaction for the com-

bustion is as follows:

One mole of methane reacts with one of carbon tetrachloride and two of oxygen to form two of carbon

dioxide and four moles of HC1. The nitrogen does not participate in the main combustion reaction. It is

“carried along” with the oxygen. The coefﬁcient, 7.52, for nitrogen is obtained by multiplying the number

of moles of oxygen participating in the chemical reaction (2) by the volumetric ratio of nitrogen and

oxygen in air (79/21). The combustion produces (2 + 4 + 7.52) = 13.52 moles of ﬂue gas. If the calculations

were performed in lb-moles, the combustor will produce 13.52 ¥ 387 = 5232 scf of ﬂue gas. If the calculation

were performed in metric units, the 13.52 g-moles of ﬂue gas would occupy at 0.02404 scm/g-mole or

0.325 m

at STP.

Stoichiometric calculations allow one to determine the amount of gas formed by the combustion

process. Thermodynamic calculations allow one to determine the temperature of the gases. The combined

material and energy balance is used to determine the temperature, gross composition, and ﬂow rates in

an incinerator or combustor. The heat balance is completely analogous to the mass balance that was

performed above. The mass balance takes advantage of the fact that matter is neither created nor destroyed

in an incinerator, that all of the elements that enter the combustor must come out, although the materials

react chemically to form different compounds. The heat balance is based on the fact that all of the energy

that goes into the incinerator will be released at some point. Because energy can ﬂow into and out of a

system in many ways, a rigorous energy balance can be time-consuming and complex. Fortunately, many

simplifying assumptions can be made.

The ﬁrst step in the heat balance is to calculate the heat input to the combustor. The heat input is

simply the sum of the sensible heat released by each component (waste and fuel) to the combustor as it

burns, or as it changes phase. The heating values of pure compounds and for fuels such as natural gas

or fuel oil can be determined by calorimetric methods or, more frequently, from tabulated heats of

formation as in Tables 13.1 and 13.2. Direct measurement of the wastes’ heating value by calorimetric

techniques is possible, but it is rarely practical. The typical laboratory calorimeter is a very small device

that can only measure the heat of combustion of a very small sample. Wastes, on the other hand, tend

to consist of large, highly inhomogeneous components. It is usually very difﬁcult to produce a sample

of the waste that represents its composition but is small enough to ﬁt in the calorimeter. While multiple

samples can be tested, the cost becomes high, and evaluation of the data becomes complex. It is recom-

mended that for critical applications, the heat of formation and anticipated waste compositions be used

to calculate the heat of combustion.

The heat of combustion or heating value of any compound can be calculated from the heat of formation

by the following formula:

(13.8)

where DH

c,298°K

is the heat of combustion at 298°K, n is the stoichiometric coefﬁcient for each of the

compounds, DH

is the heat of formation of each compound, and the subscripts p and r refer, respectively,

to the compounds that are the products and reactants.

The following example showing how the heat of combustion of 1,3-dichloropropane (liquid) is cal-

culated from the heat of formation. Table 13.1 gives its heat of formation as 388 Btu/lb and its molecular

weight at 179. The combustion equation is as shown below:

CH CCl O N CO HCl N H

c442 2 2 2

2752 2 4 752+++ Æ + + +..D

DSDSDHnHn(H)

cK f f,

()

298∞

pprr

13-20 The Civil Engineering Handbook, Second Edition

TA BLE 13.1 Heats of Formation and Combustion of Pure Compounds

Reference condition, 1 atmosphere, 25°C, 77°F

Heat of Formation Higher Heating Value Lower Heating Value

Mol. Cal/ Btu Cal/ Btu/ Cal/ Btu/

Compound Formula Weight g-mol Cal/g lb-mole Btu/lb g-mol Cal/g lb-mole Btu/lb g-mol Cal/g lb-mole Btu/lb

Saturated, Paraﬁns, Alkanes

Methane CH

16 17,889 1,118 23,200 2,013 212,797 13,300 383,035 23,940 191,759 11,985 345,166 21,573

Ethane C

30 20,234 674 36,421 1,214 372,821 12,427 671,078 22,369 341,264 11,375 614,275 20,476

Propane C

44 24,820 564 44,676 1,015 530,604 12,059 955,087 21,707 488,528 11,103 879,350 19,985

n-Butane C

58 30,150 520 54,270 936 687,643 11,856 1,237,757 21,341 635,048 10,949 1,143,086 19,708

n-Pentane C

72 35,000 486 63,000 875 845,162 11,738 1,521,292 21,129 782,048 10,862 1,407,686 19,551

n-Hexane C

86 39,960 465 71,928 836 1,002,571 11,658 1,804,628 20,984 928,938 10,802 1,672,088 19,443

Each C past C

14 4,925 352 8,865 633 157,444 11,246 283,399 20,243 146,925 10,495 264,465 18,890

Unsaturated Compounds, Alkenes

Ethylene C

28 (12,496) (446) (22,493) (803) 337,234 12,044 607,021 21,679 316,196 11,293 569,153 20,327

Propylene C

28 (4,879) (116) (8,782) (209) 491,986 11,714 885,575 21,085 460,429 10,963 828,772 19,733

1-Butene C

56 30 1 54 1 649,446 11,597 1,169,003 20,875 607,370 10,846 1,093,266 19,523

1-Pentene C

70 5,000 71 9,000 129 806,845 11,526 1,452,321 20,747 754,250 10,775 1,357,650 19,395

1-Hexene C

84 9,650 115 17,370 207 964,564 11,483 1,736,215 20,669 901,450 10,732 1,622,610 19,317

Each C past C

14 4,925 352 8,865 633 157,444 11,246 283,399 20,243 146,925 10,495 264,465 18,890

Other Organic Compounds

Acetaldehyde C

OH 43 36,760 925 71,568 1,664 25,820 5,833 451,475 10,499 235,041 5,466 423,074 9,839

Acetic Acid C

COOH 73 116,400 1,595 209,520 2,870 242,497 3,322 436,494 5,979 216,199 2,962 389,158 5,331

Acetylene C

26 (54,194) (2,084) (97,549) (3,752) 310,615 11,947 559,107 21,504 300,096 11,542 540,173 20,776

Benzene C

78 (19,820) (254) (35,676) (457) 789,083 10,116 1,420,349 18,210 757,526 9,712 1,363,547 17,481

Benzene (L) C

78 (11,720) (150) (21,096) (270) 780,983 10,013 1,405,769 18,023 749,426 9,608 1,348,967 17,294

1,3-Butadiene C

54 (26,330) (488) (47,394) (878) 607,489 11,250 1,093,480 20,250 575,932 10,665 1,036,678 19,198

Cyclohexane C

84 37,340 445 67,212 800 936,874 11,153 1,686,373 20,076 873,760 10,402 1,572,768 18,723

Ethanol C

OH 98 46,240 574 101,232 1,033 336,815 3,437 606,267 6,186 305,258 3,115 549,464 5,607

Ethanol (L) C

OH 46 66,356 1,443 119,441 2,597 326,669 7,102 588,058 12,784 285,142 6,416 531,256 11,549

Ethylbenzene C

106 (7,120) (67) (12,816) (121) 1,101,121 10,388 1,982,018 18,698 1,048,526 9,982 1,887,347 17,805

Ethylene glycol (L) C

(OH)

62 (108,580) (1,751) (195,444) (3,152) 501,635 8.091 902,943 14,564 470,078 7,582 846,140 13,647

Methanol CH

OH 32 12,190 381 21,942 686 218,496 6,828 393,293 12,290 197,458 6,171 355,424 11,107

Methanol (L) CH

OH 32 48,100 1,503 86,580 2,706 182,586 5,706 328,655 10,270 161,548 5,048 290,786 9,087

Incinerators 13-21

Methylcyclohexane C

98 57,036 582 102,665 1,048 1,079,547 11,016 1,943,185 19,828 1,005,914 10,264 1,810,645 18,476

Methylcyclohexane (L) C

98 36,990 377 66,582 679 1,099,593 11,220 1,979,267 20,197 1,025,960 10,469 1,846,728 18,844

Styrene C

104 45,450 437 81,810 787 980,234 9,425 1,764,421 16,966 938,158 9,021 1,688,684 16,237

To l u e ne (methylbenzene) C

92 (11,950) (130) (21,510) (234) 943,582 10,256 1,698,448 18,461 901,506 9,799 1,622,711 17,628

To luene (methylbenzene) (L) C

92 (2,820) (31) (5,076) –55.2 934,452 10,157 1,682,014 18,283 892,376 9,700 1,606,277 17,460

Inorganic Compounds

Ammonia NH

17 11,040 649 19,872 1,169 91,436 5,379 164,584 9,681 75,657 4,450 136,183 8,011

Carbon dioxide CO

44 94,052 2,138 169,294 3,848 0 0 0 0 0 0 0 0

Carbon monoxide CO 28 26,416 943 47,549 1,698 67,636 2,416 121,745 4,348 67,636 2,416 121,745 4,348

Hydrogen chloride HCl 36.5 22,063 604 39,713 1,088 0 0 0 0 0 0 0 0

Hydrogen sulﬁde H

S3448,15 142 8,667 255 134,462 3,955 424,032 7,119 123,943 3,645 223,097 6,562

Nitrogen oxides NO 30 (21,600) (720) (38,880) (1,296) 21,600 720 28,880 1,296 21,600 720 38,880 1,296

O44(8.041) (183) (14,474) (329) 8.041 183 14,474 329 8,041 183 14,474 329

46 (19,490) (424) (35,082) (763) 19,490 424 35,082 763 19,490 424 35,082 763

92 (2,309) (25) (4,156) (45.2) 2,309 25 4,156 45 2,309 25 4,156 45

Sulfur dioxide SO

46 70,960 1,543 127,728 2,777 0 0 0 0 0 0 0 0

Sulfur trioxide SO

80 94,450 1,181 170,010 2,125 (23,490) (294) (42,282) (529) (23,490) (294) (42,282) (529)

Sulfur trioxide (L) SO

80 104,800 1,310 188,640 2,358 (33,840) (423) (60,912) (761) (33,840) (423) (60,912) (761)

Wate r H

O1857,798 3,211 104,036 5,780 10,519 584 18,934 1,052 0 0 0 0

Wate r (L) H

O1868,317 3,795 122,971 6,832 0 0 0 0 (10,519) (584) (18,934) (1,052)

Chlorinated Organics

Methylene chloride (L) CH

CL 50.5 22,630 448 40,734 807 161,802 3,204 291,244 5,767 151,283 2,996 272,309 5,392

Dichloromethane (L) CH

95 22,800 268 41,040 483 115,378 1,357 207,680 2,443 115,378 1,357 207,680 2,443

Chloroform (L) CHCl

119.5 24,200 203 43,560 365 67,724 567 121,903 1,020 67,724 567 121,903 1,020

Carbontetrachloride (L) CCl

154 24,000 156 43,200 281 21,670 141 39,006 253 21,670 141 39,006 253

Ethyl chloride C

Cl 64.5 26,700 414 48,060 745 320,101 4,963 576,182 8,933 299,063 4,637 538,313 8,346

1,1-Dichlorethane (L) C

99 31,050 314 55,890 565 269,497 2,722 485,095 4,900 258,978 2,616 466,160 4,709

1,1,2,2-Tetrachloroethane (L) C

168 36,500 217 65,700 391 171,539 1,021 308,770 1,838 171,539 1,021 308,770 1,838

Monochloro-n-propane (L) C

Cl 78.5 31,100 396 55,980 713 478,070 6,091 860,526 10,962 446,513 5,688 803,723 10,239

1,3-Dichloropropane (L) C

Cl 179 38,600 216 69,480 388 424,316 2,370 763,769 4,267 403,278 2,253 725,900 4,055

1-Chlorobutane (L) C

Cl 92.5 35,200 381 63,360 685 636,339 6,879 1,145,410 12,383 594,263 6,424 1,069,673 11,564

1-Chloropentane (L) C

Cl 106.5 41,800 392 75,240 706 792,108 7,438 1,425,794 13,388 739,513 6,944 1,331,123 12,499

1-Chloroethylene (L) C

Cl 62.5 8,400 134 15,120 242 270,084 4,321 486,151 7,778 259,565 4,153 467,217 7,475

trans-1,2-Dichloro

ethylene (L)

101 100 10 1,800 17.8 367,864 3,642 662,155 6,556 346,826 3,434 624,287 6,181

Tr ichloroethylene (L) C

HCl

131.5 1,400 11 2,520 19.2 184,576 1,404 332,237 2,527 184,576 1,404 332,237 2,527

Te t r a c hloroethylene (L) C

166 3,400 20 6,120 36.9 136,322 821 245,380 1,478 136,322 821 245,380 1,478

13-22 The Civil Engineering Handbook, Second Edition

TA BLE 13.1 (continued) Heats of Formation and Combustion of Pure Compounds

Reference condition, 1 atmosphere, 25°C, 77°F

Heat of Formation Higher Heating Value Lower Heating Value

Mol. Cal/ Btu Cal/ Btu/ Cal/ Btu/

Compound Formula Weight g-mol Cal/g lb-mole Btu/lb g-mol Cal/g lb-mole Btu/lb g-mol Cal/g lb-mole Btu/lb

3-Chloro-1-propene (L) C

Cl 76.5 150 2 270 3.53 440,703 5,761 793,265 10,369 419,665 5,486 755,397 9,874

monochlorobenzene (L) C

112.5 12,390 110 22,302 198 710,619 6,317 1,279,114 11,370 689,581 6,130 1,241,246 11,033

p-dichlorobenzene (L) C

147 5,500 37 9,900 67.3 671,255 4,566 1,208,259 8,219 660,736 4,495 1,189,325 8,091

Hexachlorobenzene (L) C

285 8,100 28 14,580 51.2 483,639 1,697 870,550 3,055 483,639 1,697 870,550 3,055

Benzylchloride C

Cl 126.5 0 0 0.0 885,378 6,999 1,593,680 12,598 853,821 6,750 1,536,878 12,149

Heat of combustion of chlorinated compounds assumes that all chlorine goes to HCl with addition of liquid water if needed.

Values in parentheses are negative.

Positive values indicate heat released from combustor.

Incinerators 13-23

The heat of formation for each of these compounds is given per unit weight and per mole, and each

compound’s molecular weight is given below:

The heat of combustion of 1,3-dichloropropane liquid is therefore,

That is, 1530 Btu are released when liquid 1,3-dichloropropane is burned and the water in the

combustion products is condensed. What happens if the water is not condensed and its latent heat not

released as when the LHV is computed? The combustion of one mole (179 pounds) of 1,3-dichloropro-

pane forms 2 moles (36 pounds) of water. The latent heat of vaporization of water at ambient temperature

is approximately 9500 cal/g-mole, 528 cal/g, 17,100 Btu/lb-mole, or 950 Btu/lb.

The LHV of 1,3-dichloropropane, when the water formed in the reaction does not condense and

release its latent heat, is 594,500 - 2(17,100) = 560,300 Btu/lb-mole of 1,3-dichloropropane burned.

Dividing this value by the compound’s molecular weight, 179, gives its lower heating value per pound,

3130 Btu/lb.

This calculation illustrates the two terms: higher heating value (HHV) and lower heating value (LHV)

for a material. The HHV corresponds to the heat released by the combustion of a compound when the

water formed condenses and gives up its latent heat. This is heating value measured in a calorimeter.

The LHV corresponds to the heat released on combustion when the water leaves the combustion chamber

in the vapor form, as occurs in an incinerator. As can be seen, the difference is quite signiﬁcant. Clearly

published heat of combustion (also called heating value) data must be used with full knowledge of

whether the value is the HHV or LHV.

Published heating value for halogenated compounds encounter a second problem inherent in calo-

rimetry. Frequently, the calorimetric determination of a compound’s heating value is made by placing

the compound into a calorimeter and adding just enough oxygen gas to completely oxidize it — termed

the stoichiometric quantity. Highly halogenated compounds, such as CC1

, CHC1

, or highly chlorinated

benzenes, do not incorporate sufﬁcient hydrogen in the molecule to form HC1. When a system contains

more moles of chlorine than hydrogen, a signiﬁcant fraction of the chlorine is converted to Cl

gas rather

than to HC1. This condition is counter to the one that occurs in an incinerator, where sources of hydrogen

are plentiful. For example, the combustion of chloroform in a calorimeter will occur by the following

chemical reaction (the heats of formation for each compound are given directly beneath the formula):

When sufﬁcient hydrogen is present, as in an incinerator, the combustion follows the following

reaction, with the corresponding free energies of formation given beneath the compounds:

(L) + 4O

Æ 3CO

+2H

O(L) + 2HCl

(Btu/lb) –3880 0 –3848 –6832 –1088

Mol. Wt. 179 32 44 18 36.5

(Btu/lb-mole) –69,500 0 –169,000 –123,000 –39,700

CHCl L O CO H O L HCl

36 2 2 2 2

43 2 2

()

+Æ +

()

Btu lb-mole or Btu lb

()

3 169 300 2 123 000 2 39 700 69 500

594 500 1 530

,,,,

CHCl O CO HCl Cl

H cal g-mole

32 2 2

24 200 0 94 052 22 063 0

91 915

+Æ + +

()

++-

()

,,,

13-24 The Civil Engineering Handbook, Second Edition

As can be seen, the heating value of a chlorinated compound that is determined in a calorimeter

without the presence of a hydrogen source, like water, is signiﬁcantly different from its actual heating

value under incinerator conditions when water and other sources of hydrogen are present. It is recom-

mended that the heats of combustion be calculated from the higher and lower heating values of the pure

components whenever possible, recognizing the facts that the water produced will never condense inside

the combustion chamber and that the chlorine will react with any source of hydrogen to form HCl. See

Theodore (1987, pp.143, 146) for a further discussion of this subject.

Waste streams can have a negative heat release in a combustion chamber. For example, if a waste

stream is pure water, then it will absorb approximately 1050 Btu/lb (its latent heat of vaporization) when

injected into an incinerator. The latent heat of vaporization of organic constituents in the waste is much

smaller than that of water (typically one-quarter to one-half that of water) and is usually included in the

tabulated heating values.

The heat of combustion of complex materials such as paper, leather, fuel oil, etc., cannot be determined

from heats of formation. Table 13.2 lists typical heating values for these types of material.

Having established the heat input rate to the incinerator, it is necessary to then determine the resultant

gas temperature. When performing material and energy calculations by hand, this is done by using the

gas composition calculated from the material balance and determining through iteration the resultant

temperature based on the composition and the enthalpy (heat content) of gases as given in Table 13.3.

When doing the calculation on a computer, one normally uses correlations of heat capacity and the

resulting enthalpy of each gas constituent.

Two correlations are typically used for calculating the enthalpy versus temperature of the components

of a ﬂue gas. One is based on the heat capacity of the gases:

(13.9)

(13.10)

and the second is based on the mean heat capacities over a speciﬁed temperature range:

(13.11)

with the enthalpy calculated by

(13.12)

The coefﬁcients for Eqs. (13.11) and (13.12) are given in Table 13.4. The coefﬁcients for Eqs. (13.9)

and (13.10) are given in Table 13.5.

The full power of a material and energy balance is illustrated in Tables 13.6 and 13.7, which show the

complete material and energy balance for an incinerator burning three waste streams (solid waste, high

Btu liquid, and low Btu liquid) and a supplemental fuel stream of #2 fuel oil. The liquid waste streams

are synthetic mixtures of components that may be used as part of a trial burn. The waste stream

compositions are shown in the upper half of the ﬁrst page of the table. As can be seen, the solid waste

stream consists of refuse contaminated with chloroform, 1,1-dichloroethane, ethylene glycol, and ethanol.

The low Btu liquid stream is water-contaminated ethylene glycol and ethanol, and the liquid waste consists

of fuel oil doped with the speciﬁc organic compounds.

CHCl O H O CO HCl

H cal g-mole

22 2

24 200 0 57 598 94 052 22 063

140 837

++Æ+

()

++-

()

,,,,

CABTCT

=+ +

-2

HATTo BT T C T T

()

[]

CABtCt Dt

p, mean

bc d

=+ + +

HC TTTdT

p, mean o

()

Incinerators 13-25

TA BLE 13.2 Selected Properties of Waste Constituents and Fuels

Waste Constituents

Proximate Analysis

(as received) Weight %

Ultimate Analysis

(Dry) Weight %

Higher Heating Value

(kcal/kg)

Moisture

Volatile Fixed Non- Non- As and

Waste Component Moisture Matter Carbon Comb. C H O N S Comb. Received Dry Ash Free

Paper and Paper Products

Paper, mixed 10.25 75.94 7.44 5.38 43.31 5.82 44.32 0.25 0.20 6.00 3778 4207 4475

Newsprint 5.97 81.12 11.48 1.43 49.14 6.10 43.03 0.05 0.16 1.52 4430 4711 4778

Brown paper 5.83 83.92 9.24 1.01 44.90 6.08 47.34 0.00 0.11 1.07 4031 4281 4333

Tr ade magazines 4.11 66.39 7.03 22.47 32.91 4.95 38.55 0.07 0.09 23.43 2919 3044 3972

Corrugated boxes 5.20 77.47 12.27 5.06 43.73 5.70 44.93 0.09 0.21 5.34 3913 4127 4361

Plastic-coated paper 4.71 84.20 8.45 2.64 45.30 6.17 45.50 0.18 0.08 2.77 4078 4279 4411

Waxed milk cartons 3.45 90.92 4.46 1.17 59.18 9.25 30.13 0.12 0.10 1.22 6293 6518 6606

Paper food cartons 6.11 75.59 11.80 6.50 44.74 6.10 41.92 0.15 0.16 6.93 4032 4294 4583

Junk mail 4.56 73.32 9.03 13.09 37.87 5.41 42.74 0.17 0.09 13.72 3382 3543 4111

Food and Food Waste

Ve getable food waste 78.29 17.10 3.55 1.06 49.06 6.62 37.55 1.68 0.20 4.89 997 4594 4833

Citrus rinds and seeds 78.70 16.55 4.01 0.74 47.96 5.68 41.67 1.11 0.12 3.46 948 4453 4611

Meat scraps (cooked) 38.74 56.34 1.81 3.11 59.59 9.47 24.65 1.02 0.19 5.08 4235 6913 7283

Fried fats 0.00 79.64 2.36 0.00 73.14 11.54 14.82 0.43 0.07 0.00 9148 9148 9148

Mixed garbage I 72.00 20.26 3.26 4.48 44.99 6.43 28.76 3.30 0.52 16.00 1317 4719 5611

Mixed garbage II — — — — 41.72 5375 27.62 2.97 0.25 21.81 — 4026 5144

Trees, Wood, Brush, Plants

Green logs 50.00 42.25 7.25 0.50 50.12 6.40 42.26 0.14 0.08 1.00 1168 2336 2361

Rotten timbers 26.80 55.01 16.13 2.06 52.30 5.5 39.0 0.2 1.2 2.8 2617 2528 2644

Demolition softwood 7.70 77.62 13.93 0.75 51.0 6.2 41.8 0.1 <0.1 0.8 4056 4398 4442

Waste hardwood 12.00 75.05 12.41 0.54 49.4 6.1 43.7 0.1 <0.1 0.6 3572 4056 4078

Furniture wood 6.00 80.92 11.74 1.34 49.7 6.1 42.6 0.1 <0.1 1.4 4083 4341 4411

Evergreen shrubs 69.00 25.18 5.01 0.81 48.51 6.54 40.44 1.71 0.19 2.61 1504 4853 4978

Balsam spruce 74.35 20.70 4.13 0.82 53.30 6.66 35.17 1.49 0.20 3.18 1359 5301 5472

Flowering plants 53.94 35.64 8.08 2.34 46.65 6.61 40.18 1.21 0.26 5.09 2054 4459 4700

Lawn grass I 75.24 18.64 4.50 1.62 46.18 5.96 36.43 4.46 0.42 6.55 1143 4618 4944

13-26 The Civil Engineering Handbook, Second Edition

TA BLE 13.2 (continued) Selected Properties of Waste Constituents and Fuels

Waste Constituents

Proximate Analysis

(as received) Weight %

Ultimate Analysis

(Dry) Weight %

Higher Heating Value

(kcal/kg)

Moisture

Volatile Fixed Non- Non- As and

Waste Component Moisture Matter Carbon Comb. C H O N S Comb. Received Dry Ash Free

Lawn grass II 65.00 — — 2.37 43.33 6.04 41.68 2.15 0.05 8.20 1964 3927 4278

Ripe leaves I 9.97 66.92 19.29 3.82 52.15 6.11 30.34 6.99 0.16 4.25 4436 4927 5150

Ripe leaves II 50.00 — — 2.37 43.33 6.04 41.68 2.15 0.05 8.20 1964 3927 4278

Wo od and bark 20.00 67.89 11.31 0.80 50.46 5.97 42.37 0.15 0.05 1.00 3833 4785 4833

Brush 40.00 — — 5.00 42.52 5.90 41.20 2.00 0.05 8.33 2636 4389 4778

Mixed greens 62.00 26.74 6.32 4.94 40.31 5.64 39.00 2.00 0.05 13.00 1494 3932 4519

Grass, dirt, leaves 21–62 — — — 36.20 4.75 26.61 2.10 0.26 30.08 — 3491 4994

Domestic Wastes

Upholstery 6.9 75.96 14.52 2.62 47.1 6.1 43.6 0.3 .1 2.8 3867 4155 4272

Tires 1.02 64.92 27.51 6.55 79.1 6.8 5.9 0.1 1.5 606 7667 7726 8278

Leather 10.00 68.46 12.49 9.10 60.00 8.00 11.50 10.00 0.40 10.10 4422 4917 5472

Leather, shoe 7.46 57.12 14.26 21.16 42.01 5.32 22.83 5.98 1.00 22.86 4024 4348 5639

Shoe, heel & sole 1.15 67.03 2.08 29.74 53.22 7.09 7.76 0.50 1.34 30.09 6055 6126 8772

Rubber 1.20 83.98 4.94 9.88 77.62 10.35 — — 2.00 10.00 6222 6294 7000

Mixed plastics 2.0 — — 1.00 60.00 7.20 22.60 — — 10.20 7833 7982 8889

Plastic ﬁlm 3–20 — — — 67.21 9.72 15.82 0.46 0.07 6.72 — 7692 8261

Polyethylene 0.20 98.54 0.07 1.19 84.54 14.18 0.00 0.06 0.03 1.19 10,932 10,961 11,111

Polystyrene 0.20 98.67 0.68 0.45 87.10 8.45 3.96 0.21 0.02 0.45 9122 9139 9172

Polyurethane 0.20 87.12 8.30 4.38 63.27 6.26 17.65 5.99 0.02 4.38(a) 6554 6236 6517