INCINERATION TUTORIAL

AN EXCERPT FROM THE PROGRAM INCINER.BAS ON THE DISK TO ACCOMPANY BASIC ENVIRONMENTAL ENGINEERING, BY H.R. BUNGAY

EDITED FOR THE WORLD WIDE WEB BY GEORGE PENDLETON AND ANNA RUEPP

MARK OWENS MAY, 1990

JAMES M. WALDRON DEC., 1992

• RELIABILITY
• SAFETY
• EFFICIENCY

AT THE SAME TIME, IT IS HIGHLY CONTROVERSIAL AND EXPENSIVE. IN PREVIOUS DECADES, LANDFILLS WERE PRIMARILY USED FOR WASTE DISPOSAL, ALLOWING NATURE TO TAKE ITS COURSE, EVENTUALLY REDUCING THE END VOLUME TOXICITY OF THE WASTES. HOWEVER, BECAUSE OF INCREASINGLY STRINGENT ENVIRONMENTAL REGULATIONS CONCERNING AIR QUALITY, LANDFILLS, AND GROUNDWATER CONTAMINATION, ALONG WITH THE DECREASING AVAILABILITY OF LAND FOR THE ENCAPSULATION OF WASTES, INCINERATION HAS BECOME THE DESIRED DISPOSAL METHOD FOR MUNICIPALITIES AND INDUSTRIES.

YET, EVEN INCINERATION TECHNOLOGY IS CONSTANTLY UNDERGOING REVISIONS IN ORDER TO MEET TOUGHER ENVIRONMENTAL STANDARDS. THESE TECHNOLOGICAL ADVANCES INCLUDE THOSE THAT INCREASE EFFICIENCY, AND THOSE THAT USE EMISSIONS CONTROL APPARATUS.

INCINERATION THERMALLY DECOMPOSES MATTER THROUGH OXIDATION, THEREBY REDUCING AND MINIMIZING THE WASTES, AND DESTROYING THEIR TOXICITY. IT CAN BE APPLIED TO INDUSTRIAL, MUNICIPAL, AND HAZARDOUS WASTES, PROVIDED THAT THEY CONTAIN ORGANIC MATERIAL. SINCE IT IS PRIMARILY ORGANIC SUBSTANCES THAT CAN UNDERGO AND SUSTAIN THERMAL DEGRADATION.

• CO
• CO2
• WATER
• ASH

DEPENDING ON THE COMPOSITION OF THE INITIAL WASTE, COMPOUNDS CONTAINING:

• HALOGENS
• METALS
• NITROGEN
• SULFUR

MAY BE PRODUCED. THESE COMPOUNDS, ALONG WITH CO, ARE DELETERIOUS TO THE ATMOSPHERE, AND HIGHLY REGULATED. PRESENTLY, THE DESTRUCTION EFFICIENCY FOR THESE HAZARDOUS WASTES MUST BE 99.9999 %. THUS, TO MEET REGULATIONS, INCINERATORS NEED TO BE EQUIPPED WITH:

• AFTERBURNERS
• SCRUBBERS
• FILTRATION UNITS
• MEMBRANES

• ROTARY KILN
• FLUIDIZED BED
• LIQUID INJECTION
• MULTIPLE HEARTH
• CATALYTIC COMBUSTION
• WASTE-GAS FLARE
• DIRECT-FLAME

OF THESE, ROTARY KILN, FLUIDIZED BED, AND LIQUID INJECTION ARE THE MOST, PREVALENT IN INDUSTRY BECAUSE OF THEIR, APPLICABILITY TO LARGE SCALE USE AND, AND THEIR VERSATILITY. CONSEQUENTLY, I WILL CONCENTRATE ON, THESE THREE KINDS.

ROTARY KILN CHARACTERISTICS:

• ROTATE WASTES IN CYLINDRICAL CONTAINER, ENABLING THOROUGH MIXING WITH AIR
• OPERATING TEMPS. FROM 1500-3000 F
• HAS GREATEST RESISTANCE TO HIGH TEMPS.
• CAN HANDLE LIQUID, SLUDGE, SOLID, OR GASES IN VERY LARGE QUANTITIES
• CAN OPERATE IN BATCH MODE, ALLOWING MORE FLEXIBILITY THAN CONTINUOUS MODE
• CAN BE MOBILE TO ALLOW ONSITE TREATMENT
• CAN ACCEPT ENTIRE DRUMS OF WASTE, A UNIQUE FEATURE

FLUIDIZED BED CHARACTERISTICS:

• VESSEL CONTAINS INERT GRANULAR MATERIAL THAT EXPANDS AND ACTS THEORETICALLY AS A FLUID WHEN GASES ARE INJECTED UP THROUGH THE MATERIAL BED FROM NOZZLES
• OPERATING TEMPS FROM 1400-1800 F
• CAN HANDLE LIQUID, SLUDGE, SOLID, OR GASES
• WASTE ENTERS THROUGH NOZZLES
• OFFERS NEARLY ISOTHERMAL OPERATION
• CAN'T HANDLE WASTES THAT MELT AND SLAG, DISRUPTING FLUIDIZATION

LIQUID INJECTION CHARACTERISTICS:

• WASTES ARE SENT THROUGH NOZZLES AND ATOMIZED INTO SMALL DROPLETS TO ALLOW FOR THE GREATEST POSSIBLE MIXING WITH AIR
• OPERATING TEMPS. FROM 1200-3000 F
• FEED MUST ACT AS A LIQUID HAVING A VISCOCITY LESS THAN 10,000 SSU
• SOLIDS ARE OKAY IF THEY CAN BE MELTED AND PUMPED
• CAN COMPLETELY COMBUST NONCOMBUSTIBLES LIKE CONTAMINATED WATER, ALONG WITH ORGANIC COMBUSTIBLE MATERIAL
• HAS A HORIZ. OR VERT. CONFIGURATION
• A SUSPENSION BURNER, THAT IS THE MOST LABORFREE AND FLEXIBLE KIND OF INCINERATOR

ONE OTHER CHARACTERISTIC THAT ALL THREE TYPES OF INCINERATORS (ROTARY KILN, FLUIDIZED BED, AND LIQUID INJECTION) SHARE IS THAT THEY CAN ALL BE OPERATED IN A PYROLYSIS OR OXYGEN STARVED MODE. WASTES WITH HIGH CALORIC VALUE THAT ARE CAPABLE OF RELEASING GREAT HEAT CONTENT ARE MOST APPROPRIATE FOR THIS KIND OF OPERATION. THE OTHER TYPES OF INCINERATORS ARE DESCRIBED AS FOLLOWS.

MULTIPLE HEARTH INCINERATORS CONSIST OF VERTICALLY SHAPED HEARTHS, AND ARE PRIMARILY UTILIZED FOR SEWAGE SLUDGE. THEY ARE OPERATED FROM 1400-1800 F. CATALYTIC COMBUSTION, WASTE-GAS FLARE AND DIRECT FLAME INCINERATORS ARE ALL FOR GASES. CATALYTIC COMBUSTORS USE A CATALYST AND ARE DESIGNED FOR LOW ORGANIC CONCENTRATION WASTES. WASTE-GAS FLARES ARE USED FOR NON-HAZARDOUS WASTE THAT HAS HIGH ORGANIC CONTENT. DIRECT FLAME INCINERATORS OPERATE FROM 1000-1500 F AND ARE USED WHEN WASTE GAS CONTAINS PARTICLES.

ON A FINAL NOTE, ONE VERY CONTROVERSIAL FORM OF INCINERATION THAT PRESENTLY HAS BEEN BANNED IN THE UNITED STATES, BUT IS USED IN EUROPE IS OCEAN INCINERATION. FOR THIS,TWO INCINERATORS ARE MOUNTED ON A HUGE SHIP THAT CARRIES THE WASTES OUT TO THE MIDDLE OF THE OCEAN AND BURNS THEM OUT THERE.THE IDEAL WASTES FOR THIS KIND OF DISPOSAL ARE TOXIC AND HAZARDOUS WASTES SUCH AS CHLORINATED MATTER, PCB'S,AND ORGANOMETALLICS. OCEAN INCINERATION IS PERFECT FOR THESE WASTES BECAUSE THE ACIDS PRODUCED CAN BE NEUTRALIZED BY THE HUGE BUFFERING CAPACITY OF THE OCEAN. THIS ELIMINATES THE NEED FOR SCRUBBERS AND OTHER SECONDARY TREATMENT TO DETOXIFY THE COMBUSTION PRODUCTS AND MAKE THEM MORE ENVIRONMENTALLY ACCEPTABLE.

KEY FEATURES OF A COMBUSTION INCINERATOR:

• WASTE STORAGE AND HANDLING
• WASTE FEEDING
• COMBUSTION
• STEAM AND ELECTRICITY GENERATION
• AIR POLLUTION CONTROL
• ASH RESIDUE HANDLING

• (1)DRYING-MOISTURE IS EVAPORATED
• (2)DEVOLATILIZATION-COMBUSTIBLE VOLATILES ARE RELEASED
• (3)IGNITION-VOLATILES ARE IGNITED IN THE PRESENCE OF O2
• (4)COMBUSTION OF FIXED CARBON-VOLATILE MATTER IS COMPLETELY COMBUSTED AND FIXED CARBON IS OXIDIZED TO CO2

1. MASS BURN-MOST COMMON

MINIMAL PREPROCESSING REQUIRED (NOT MUCH SIZING, SHREDDING, ETC.). MASS BURN INCINERATORS VARY IN SIZE. THEY RANGE FROM 100 TO 1000 TONS OF WASTE PER DAY. USE A GRATE SYSTEM TO MIX AND AGITATE THE WASTE AS IT TRAVELS THROUGH THE FURNACE TO PROVIDE COMPLETE COMBUSTION. AIR FOR COMBUSTION IS SUPPLIED BY FANS OR BLOWERS UNDER AND OVER THE GRATES.

THREE TYPES OF MASS BURN INCINERATORS (BASED ON ENERGY RECOVERY METHOD)

(A)WATER WALL FURNACE

• ENERGY IS RECOVERED BY STEEL TUBES FILLED WITH WATER WHICH LINE THE COMBUSTION CHAMBER

• ENERGY IS RECOVERED BY A WASTE HEAT BOILER LOCATED AFTER THE COMBUSTION CHAMBER

• SIMILAR TO A REFRACTORY FURNACE, BUT USES A ROTATING COMBUSTION CHAMBER 2. MODUAL COMBUSTOR
  • TYPICALLY SMALLER THAN MASS BURN INCINERATORS
  • 25 TO 120 TONS/DAY
  • VERY LITTLE PREPROCESSING INVOLVED
  • WASTE IS FED INTO FURNACE BY A HORIZONTAL, HYDRAULIC RAM

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  3. FLUIDIZED BED COMBUSTOR
  • LIMITED EXPERIENCE WITH MIXED SOLID WASTE
  • PREHEATED AIR, UNDER PRESSURE, IS FORCED THROUGH A BED OF SAND, CAUSING THE SAND TO EXPAND.
  • MIXED SOLID WASTE IS FED ONTO THE SAND BED, WHERE COMBUSTION TAKES PLACE

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  NON-COMBUSTION TECHNIQUES-OXYGEN DEFICIENT

  (LIMITED USE IN THE US)

  1. BIOGASIFICATION

  MIXED SOLID WASTE IS PLACED INTO AN ANAEROBIC DIGESTOR TO REDUSE ITS VOLUME AND TO PRODUCE METHANE. THE PROCESS INVOLVES:

  • (A)PREPROCESSING-THE ORGANIC MATERIAL IS SEPARATED FROM THE WASTE STREAM, SHREDDED, AND PLACED INTO A SLURRY
  • (B)DECOMPOSITION-THE SLURRY IS PLACED IN AN ANEROBIC DIGESTOR FOR 5-30 DAYS
  • (C)GAS COLLECTION-METHANE GAS IS COLLECTED AND REFINED FOR COMBUSTION
  • (D)LESS VOLUMINOUS DEGESTED PRODUCT IS DISPOSED OF

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  2. PYROLYSIS

  USES HEAT TO DECOMPOSE THE MIXED SOLID WASTE IN AN O2-DEFICIT OR O2-FREE ENVIRONMENT. THE PRODUCTS OF PYROLYSIS INCLUDE COMBUSTIBLE GASES AND VARIOUS SOLIDS THAT ARE DIFFICULT TO MANAGE.

  COMBUSTION FUNDAMENTALS

  THE FOLLOWING REACTIONS TAKE PLACE FOR COMBUSTION OF FUELS CONTAINING C, H, AND S (IN ORDER OF OCCURRENCE):

  • H2+H2+O2-->H2O+H2O
  • 2C+O2-->CO+CO
  • CO+CO+O2-->CO2+CO2
  • S+O2-->SO2

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  THE OPTIMAL TEMPERATURE FOR COMBUSTION OF MIXED SOLID WASTE IS IN THE RANGE FROM 1400-1600 DEGREES F.

  AIR REQUIREMENTS FOR COMBUSTION:

  STOICHIOMETRIC AMOUNT OF AIR OR O2 IS THE AMOUNT OF AIR OR O2 REQUIRED BASED ON STOICHIOMETRY. SOMETIMES, EXTRA AIR OR O2 IS REQUIRED FOR COMPLETE COMBUSTION. THIS IS EXPRESSED AS EXCESS AIR OR O2. TYPICAL EXCESS AIR REQUIREMENTS ARE 80-50% OF THE THEORETICAL OR STOICHIOMETRIC DEMAND. ON THE AVERAGE, 6-10 POUNDS OF AIR ARE REQUIRED TO COMBUST ONE POUND OF WASTE.

  THE AMOUNT OF THEORETICAL OXYGEN NEEDED CAN BE FOUND BY BALANCING THE CHEMICAL REACTION. AN EASY-TO-USE FORMULA HAS BEEN DEVELOPED TO DETERMINE VOLUME OF THEORETICAL O2 NEEDED TO COMBUST A FUEL OR WASTE WHICH CONTAINS C, H, S, AND O:

  O2 (CUBIC FT.)/LB OF FUEL = 395((C/12)+(H/4)+(S/32)-(O/32))

  C, H, S, AND O ARE THE DECIMAL FRACTIONS OF THAT ELEMENT IN ONE POUND OF THE FUEL (DRY WEIGHT). IN NEW YORK STATE, INCINERATION WITH ENERGY RECOVERY COMES RIGHT AFTER RECYCLIND AND BEFORE LANDFILLING ON ITS SOLID WASTE MANAGEMENT HIERARCHY LIST. USED PROPERLY AND SAFELY, INCINERATION CAN BE AN EFFECTIVE WAY TO DISPOSE OF OUR WASTE WHILE PRODUCING A VALUABLE FORM OF ENERGY.

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  THE MAIN PURPOSE OF INCINERATION IS TO REDUCE THE VOLUME OF SOLID WASTE, BUT THERE ARE MORE SPECIFIC INCINERATORS THAT BURN OFF DANGEROUS ORGANIC POLLUTANTS OR HOSPITAL WASTES. THERE IS ALSO THE POSSIBILITY OF ENERGY RECOVERY WITH THE ADDITION OF A BOILER. INCINERATION ITSELF IS A CONTROVERSIAL TOPIC THESE DAYS. HERE ARE SOME OF THE PROS AND CONS:

  PROS:

  • WASTE VOLUME REDUCTION
  • DESTRUCTION OF COMBUSTIBLE TOXINS
  • DESTRUCTION OF PATHOGENICALLY CONTAMINATED MATERIAL
  • ENERGY RECOVERY

  CONS:

  • AIR POLLUTION PROBLEMS
  • ASH MUST BE LANDFILLED AND MAY BE HAZARDOUS
  • HIGH CAPITAL AND OPERATION COSTS
  • WASTEWATER PROBLEMS

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  TYPES OF INCINERATORS:

  COMMERCIAL OR INDUSTRIAL INCINERATORS-

  • USUALLY SPECIFIC OR 'TAILOR-MADE'
  • MORE CONSISTANT WASTE STREAM
  • HIGHER TEMPERATURES MAY BE NECESSARY
  • STANDARDS FOR DESTRUCTION OF HAZARDOUS WASTE ARE SET AT THOSE THAT WILL DESTROY PCB'S (POLYCHLORINATED BIPHENOLS).

  MUNICIPAL INCINERATORS-

  • MORE COMMON
  • LESS CONSISTENT WASTE STREAM
  • PRE-TREATMENT (SHREDDING, DRYING, ETC.) IS USUALLY NECESSARY
  • BATCH OR CONTINUOUSLY LOADED

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  NOW, IT'S TIME FOR A QUIZ!

  1. WHICH INCINERATING PROCESS USES A HYDRAULIC RAM TO FEED THE WASTE INTO THE COMBUSTION UNIT?

  • MODUAL COMBUSTOR
  • REFRACTORY COMBUSTOR
  • ROTARY KILN FURNACE
  • WATER WALL FURNACE

  2. WHICH PROCESS USES HEAT TO DECOMPOSE MIXED SOLID WASTE IN AN O2-DEFICIT OR O2-FREE ENVIRONMENT?

  • BIOGASIFICATION
  • MODUAL COMBUSTION
  • PYROLYSIS
  • ROTARY KILN FURNACE

  3. THE OPTIMAL TEMPERATURE FOR COMPLETE COMBUSTION OF MIXED SOLID WASTE IS 3000 DEGREES F (TRUE OR FALSE??)

  4. GIVEN A FUEL WITH A CHAMICAL COMPOSITION OF 75%C, 10%H, 5%S, AND 10%O, THE VOLUME OF THEORETICAL O2 NEEDED TO COMBUST THIS FUEL IS...

  • 16.3 CUBIC FEET/LB.FUEL
  • 20.9 CUBIC FEET/LB.FUEL
  • 65.4 CUBIC FEET/LB.FUEL

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  ANSWERS:
  • 1. A MODULAR COMBUSTOR USES A HYDRAULIC RAM TO FEED THE WASTE INTO THE COMBUSTION UNIT.
  • 2. PYROLYSIS IS A PROCESS WHICH USES HEAT TO DEXOMPOSE MIXED SOLID WASTE IN AN O2-DEFICIT OR O2-FREE ENVIRONMENT.
  • 3. FALSE-THE OPTIMAL TEMPERATURE FOR COMPLETE COMBUSTION OF MIXED SOLID WASTE IS 1400-1600 DEGREES F.
  • 4. 65.4 CUBIC FEET/LB FUEL

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  LAST UPDATE:DECEMBER 14, 1994

  PLEASE DIRECT COMMENTS AND QUESTIONS TO:

  ANNA C. RUEPP

  rueppa@rpi.edu

  GEORGE PENDLETON