INCINERATION OF HAZARDOUS ORGANIC WASTES

YEN-HSIUNG KIANG Trane Thermal Company Conshohocken, Pennsylvania

ABSTRACT

This paper presents the state of the art of in­ cineration technology which consists of three major discussions: waste material, incineration system hardware and incinerator design parameters. Understanding of waste classification is necessary to ensure proper selection and design of the system. A brief presentation of different components of an incineration system are included. Finally, the importance of mixing as a design parameter is illustrated by pilot test results.

Incineration is a practical and efficient method to dispose of hazardous organic wastes. Included in the discussions of this paper are 'waste classifica­ tion, incineration system hardware and process design parameters. A pilot test was performed to study the effect of mixing on the combustion ef­ ficiency and destruction efficiency. INTRODUCTION

WASTE CLASSIFICATION

Incineration is a high temperature thermal oxidation process which can be used to convert toxic and hazardous organic or partially organic wastes into inorganic matter. Since passage of the Toxic Substances Control Act (TSCA) and the Re­ source Conservation and Recovery Act (RCRA) by Congress in 1976, incineration has become a popular technology for the disposal of chemical wastes 'containing hazardous organics. The primary advantage of using a properly de­ signed incineration system for waste disposal is the "ultimate disposal" of organic hazardous waste. The only disadvantage of incineration application is the energy requirement. However, this disadvant­ age is being gradually eliminated through the use of heat recovery equipment in incineration systems [1] . A properly designed "incineration system" consists of not only an incinerator, which oxidizes organic matter, but also heat and product recovery equipment as well as necessary air and water pollu­ tion control systems [2] .

Based on the thermal ratings, there are two basic waste classifications: 1. Combustible Waste - This group consists of wastes which will maintain required incineration temperature and sustain combustion without auxiliary fuel usage. 2. Noncombustible Waste - For this group, auxiliary fuel is required to maintain incineration temperature and sustain combustion. The distinction between combustible and non­ combustible wastes depends on the selection of incineration equipment. For example, a fluidized bed incinerator requires 1400F (762C) incineration temperature whereas a liqUid injection incinerator requires 1800F (982C) incineration temperature. Thus, a liquid waste with an adiabatic oxidation temperature of 1600 F (867 C) is classified as combustible waste when a fluidized bed incinera­ tor is used and a noncombustible waste when a liquid injection incinerator is used.

93

components of the system will be discussed in this section.

Another classification method uses the chem­ ical make-up of the waste to define it. The six chemical groups which may be used are:

INCINERATION EQUIPMENT

a. Salt Compound such as sodium and potassium compounds

There are several types of incineration equip­ ment. Details of the equipment are available else­ where [2,8,9] , only a brief description is present­ ed below.

b. Heavy Metals such as lead, selenium, arsenic and mercury c. Halogen Compound such as fluorine, chlorine, bromine and iodine

LIQUID INJECTION INCINERATOR

d. Nitrogen Compound

This type of equipment is used to dispose of liquid waste and, sometimes, slurries. It consists of a burner and a secondary chamber. The com­ bustible wastes and fuel, if required, are introduc­ ed through the burner. Noncombustible wastes usually bypass the burner and are atomized into the secondary chamber. The chamber is usually cyclindrical and can be in horizontal or vertical (upfired or downfired) orientation, depending on the chemical constituent of the waste. The mix­ ing between the secondary waste and hot exhaust gas from the burner is a critical design parameter. Uquid injection design is also very important [2, 10] .

e. Sulfur Compound f. Phosphorus and others such as boron, etc. The thermal classification determines the energy requirement, system thermal rating, equipment sizing and, partially, equipment selection. The chemical classification determines the hardware configuration, chemical and energy recovery pos­ sibility, air and water treatment systems [3-7] . INCINERATION SYSTEMS

Illustrated in Fig. 1 is the schematic of a gen­ eralized incineration system which includes the possible components of a waste incineration sys­ tem. The actual system, which may contain one or more of the components, is usually dependent upon each individual application requirement. The

FUME INCINERATOR

This group of incinerators is similar to the liquid injection incinerators. The wates are in their gas-

HEAT RECOVERY EMISSION MEDIUM AIR

WASTE FUEL

HEAT

INCINERATOR

-

RECOVERY SYSTEM

MEDIUM

UM

I

ME

1

CONTROL

QUENCH

1

EMISSION

QUENCH

-

SYSTEM-

-

CONTROL SYSTEM

J

EFFLUENT CONTROL

SYSTEM

1

LIQUID OR SOLID DISCHARGE

FIG. 1 GENERALIZED WASTE INCINERATION SYSTEM

94

r--

CLEAN

GAS

TO EXHAUST STACK

eous phase. The basic design principles are identical to liquid injection incinerator.

CATAL YTiC INCINERATOR

Catalytic incinerators are usually used for fume incineration. The catalysts are very sensitive to temperature overheating and impurity poisoning.

FLUIDIZED BED INCINERATOR

The oxidation reaction is achieved inside a bed of hot solid material into which the waste is introduced. The bed material can be inert alumina or sand.'1f the waste contains salts, the salts can also be used as the bed material and a continuous bleed of bed material is necessary to avoid build­ up. This type of incinerator is particularly suited to sludges and to some salty wastes, since the salt material will stay in the bed and can be removed as ash. When handling salty wastes, the incinera­ tion temperature is a critical design parameter to maintain bed fluidization. The bed material can be used to control stack halogen, sulfur and phos­ phorus emissions.

MULTlPLE HEARTH INCINERATOR

This type of incinerator is designed for low calorific value waste disposal. It is a vertical, cylin­ drical, and refractory lined furnace with a moving shaft in the center. Wastes are introduced from the top of the furnace or can be introduced into any one of the rotating plates. It is primarily used for the disposal of wastes which are difficult to burn or for the recovery of metals which are contained in the wastes. A more detailed illustration of the incineration equipment is available through References [8, 9] . HEAT RECOVERY

To minimize energy losses, heat recovery should be considered as part of an incineration system. The risks associated with heat recovery also must be evaluated. For clean wastes, heat recovery can be achieved through steam generation, air preheating and water heating. If the wastes contain halogens, sulfurs, or phosphorus, which generate acid after combustion, a dewpoint study must be performed to avoid condensation and corrosion of heat recovery equip­ ment. For wastes generating only solid particulates, a conventional boiler with soot blowers can be used. For salty wastes, the best form of heat re­ covery is through waste preconcentration. If steam generation is required, the molten salts produced by combustion must be solidified before entering the boiler.

ROTARY KILN

•

A rotary kiln is usually large and, thus, expen­ sive. The system is usually designed with induced draft. It is primarily used to dispose of solid wastes and sludges. However, liquid and gaseous wastes can also be handled. Rotary kiln incinerator re­ quires a secondary combustion chamber to en­ hance oxidation of the organic matter. CYCLONIC INCINERATOR

This system contains a cylindrical, refractory lined chamber. Air, wastes, and fuel are injected through the sides of the incinerator at different stages. The cyclonic motion of the air provides the mixing action required for combustion. The incinerator is a "staged combustion" unit.

CHEMICAL RECOVERY

MUL TlPLE CHAMBER (CONTROLLED AIR)

There are commercially available chemical re­ covery processes, such as hydrogen chloride re­ covery [5,11] and salt recovery [3] . By careful study and design, the incineration system can be used to recover almost any inorganic chemical which is generated through combustion [2] .

INCINERATOR

Typically, a multiple chamber incinerator is used for solid waste incineration and not suitable for flowable materials. The upper limit of this type of unit is 3900 lb/hr (I 800 kg/h). The unit con­ sists of two or more chambers. The primary cham­ ber is used to pyrolyze solid wastes and the sec­ ondary chamber is used to ensure complete com­ bustion.

EMISSION CONTROL

If the gaseous effluent-of the incinerator con-

95

erator by alkali compound injection. This process turns a gas removal problem into a solid removal problem.

tains undesirable compounds, air pollution con­ trol equipment is required to remove these com­ pounds. The solid and liquid effluents from the air pollution control system may require further treatment prior to their ultimate disposal. The selection of air pollution control equipment is a function of the chemical constituents in the waste.

NITRATED COMPOUNDS

The problem involved with nitrated compounds is the formation of nitrogen oxides. To reduce NO x formation, a two stage combustion system can be used. The first stage is designed to be operated with fuel rich condition. The unburned hydrocarbons are then oxidized in the secondary chamber. An alternate approach is to use a large combustion chamber with long residence time and a low combustion temperature on the order of 1800-2000 F ( 1000-1 100C). Besides combus­ tion modification, catalytic NOx abatement sys­ tem can be used to reduce stack NOx emission.

SALT COMPOUND

Once the organic compounds,haye been oxidiz­ ed, the salt compound will exit the incinerator chamber in a molten state or, sometimes, in a solid state. The treatment of solid particles is the same as heavy metal compounds and will be discussed later. The molten salt compounds, when cooling, usually pass through a "sticky" zone. Thus, care must be taken to avoid the sticky coating on the inside of the systems. Usually, a water quench system can be used to cool the exhaust gas to its adiabatic end point. A high energy venturi scrub­ ber is then used for removing the solidified salts. To minimize the energy requirement for particu­ late removal, adiabatic direct cooling of the ex­ haust gas with subsequent dry electrostatic pre­ cipitation or bag filtration can also be used. Since it is difficult to control the moisture content in the system, dry collection systems usually have problems. An alternative approach is to use wet electrostatic precipitation or ionized scrubbers. Although this type of equipment offers low energy consumption, its capital cost is high.

SULFUR COMPOUNDS

Sulfur dioxide is produced when burning this type of waste. Caustic scrubbing is required to en­ sure clean stack emission!!. PHOSPHORUS AND OTHER COMPOUNDS

Each individual compound has to be studied to determine the best air pollution control system requirement. INCINERATOR DESIGN PARAMETERS

HEAVY METAL COMPOUNDS

Heavy metals usually form solid particles in the combustion zone. The commonly used flue gas treatment systems are bag filters and electrostatic precipitators. The collected metals and metal oxides can be recovered or land filled. HALOGEN COMPOUNDS

Wastes containing these type of compounds are the most common among industrial wastes. The combustion of halogenated organics usually generates halogen acids and free halogens. Acids can be easily removed with a packed bed absorber. Caustic solution is required to remove free halo­ gens. One exception to the above rule is that iodine usuaUy forms free iodine in the incinerator, neces­ sitating the use of solid particulate removal equip­ ment. Halogens can also be neutralized in the incin-

96

There has been much discussion [12] on the need to specify incinerator design parameters. EPA is trying to deSignate temperatures and residence times in incinerators handling hazardous wastes by suggesting that it be part of the proposed law. The minimum requirements for hazardous organic waste incinerator operation are 1832 F ( 1000 C), 2 sec residence time and 3 percent stack oxygen. Besides the "design parameters", EPA has also specified the "combustion efficiency" e CE) and "destruction efficiency" (DE) as defined in the following equations: CE

Ceo2 =

----= :..._

__

x 100

Ceo 2 + Ceo where Ceo 2

Ceo

concentration of CO2 in exhaust gas concentration of CO in exhaust gas

and Win - Wout

DE

----

2. To direct the waste into the incinerator at a specific location with a specific pattern and with sufficient kinetic energy. Thus, an atomizer plays an important role in the mixing system design. Test data, which illus­ trates the effect of an atomizer on combustion efficiency,are also presented.

x 100

W-ID

where Win

W out

-

=

mass feed rate of the principal toxic components of waste going into the incinerator mass emission rate of principal toxic components in waste in the incinerator combustion zone

STUDY OF MIXING

In order to study the effect of mixing char­ acteristics, a pilot test was performed at Trane Thermal Company.

The requirements are 99.9 percent CE and 99.99 percent DE. Although time, temperature, stack oxygen, combustion and destruction efficiencies have been specified as the incinerator design parameters, they are meaningless without considering one other process design parameter - "mixing" . Unfortun­ ately, mixing has always been neglected in system specifications because it is not a readily defmable parameter. Usually, mixing system design is an art and has to be developed through experience. In liqUid waste disposal, atomizers are required to inject the waste into the combustion zone. The purposes of an atomizer are: 1. To break up the liquid wastes into fine drop­ lets, and

TEST INCINERATOR

The incinerator used for the test was a Trane Thermal Sub-X(R) incineration system as schema­ tically illustrated in Fig. 2. The pilot unit is the smallest size commercial unit. The heat duty of this unit is 1.3 million Btu/hr (1.37 GJ/h) utilizing a Trane Thermal Vortex Burner. The physical con­ figuration of the test unit is illustrated in Fig. 3. The burner is fired horizontally into the cylindrical incineration chamber. Wastes are atomized and sprayed down from the top of the incinerator into

FUEL

AIR

WASTE

/

STACK BURNER

---....c:::::t INJECTOR

" �OR

DEMISTER VENTURI SCRUBBER

WATER WATER -----_

SUB-X(R) TANK

DEMISTER

BLEED

BLEED

( FIG.2 SCHEMATICS OF TRANE THERMAL COMPANY SUB-x R) SYSTEM

97

\Q ex>

1.37

(710) (710) (710)

(2300)

(2300) (2300) (2300)

300 300 300

3200

3200

3200

1000

1000

1000

1000

1000

1000

1000

1000

A

A

A

B

B

B

A

A

A

A

A

A

A

A

A

A

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

98.21 98.94 99.76 99.64 99.47 99.87

49 79 122 27

880 1140 950

(952)

95.30

1745

99.87 99.87 99.91

(988) (955)

1750

(1027)

1880 1810

(977)

1790

148

15

(2300)

6.7

99.71 57

1.60

99.79 99.91 19 233

5.5

1.60

1000

149

4.0

1.50

(2300) (2300)

1000

99.85 99.69

49 170

4.0

1.50

99.80

42 (874)

(2300)

99.65

71 575 445

(835)

1605

1535

6.28 5.97

1.40

1759

6.6

1.50 1.60

133

(955)

1850

4.17

1.50

99.44

99.45

99.87

99.22

99.00

(983) (1010)

1800

4.76

1.50

(2300)

1750

99.83

222

95.86 97.97 96.36

602 5480

99.50 99.54

(983)

4830

4060

36

410

1800

(983)

(983)

39

435

99.81

99.81

174

99.80

95.35 99.55

99.88

219

(2300)

5.0

1800 1800

(983) (983)

94.41 99.89

240

34

94.11

99.20 99.87

1155

94.94

94.22 94.30

99.29 98.95

Efficiency

Combustion

1275

Efficiency

Destruction

1854

ppm/v·

5.0

1.35

(7535)

5.0

1800 1800

390

4200

4600

Total Hydrocarbon

1.50

1.41

5.6

5.1

1.39 1.39

5.4

1.37

(7535)

(7535)

(917)

1682

5.4

1.15

(3140)

1350

A

6 (983)

(916)

1680

6.0

1.16

(3140)

1350

A

5 1800

5100

(923)

1693

6.1

1.14

(3140)

1350

A

4

5.4

5300

(917)

1682

5.4

0.64

(3140)

1350

A

3

5200 5200

(923) (916)

1693 1680

6.1 6.0

0.64 0.65

(3140)

ppm/v·

C

(3140)

F

1350

02

1350

%

CO

A

Btu/lb (kJ/kg)

Time

A

Configuration

Incineration Temperature

Residence

Waste High

Heating Value

2

No.

Run

TABLE 1 PILOT TEST DATA AND RESULTS

\0 \0

'ppm/v:

parts per million by volume

1.47 4.96

1790

(977)

(7110)

3000

C

43

1014

(971 )

1779

4.4

1.17

(7110)

3000

C

42

0

(1144)

2090

0.72

0.91

(7110)

3000

C

41

0

(1144)

2090

1.9

0.89

(7110)

3000

C

40

0

(1144)

2090

1.6

0.95

(7110)

3000

C

39

(983)

1800

3000

C

38

95

51

135


99.99

99.99 10

15

> 99.99

10 135

4.0

(7110)

3000

C

37

1.05


99.99

10 220


99.99

10

99.99

1.39

(7110)

3000

C

36

(983)


99.99

10