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What is incineration?
For our purposes this is the application of combustion in the cremation process
What are cremators?
A type of incinerator that provides for a controlled combustion process witht he purpose of reducing human remains to CO2, water vapor and small, non combustible residues.
Combustion requires 3 things in the right proportions:
Oxygen, heat and fuel
What is the most common oxidizer?
Oxygen
Fuel is most commonly…
hydrocarbon based
How does a fire start?
-combustible material in combination with a sufficient quantity of oxygen is exposed to an external ignition source above the flash point for the fuel and oxidizer mix
-molecules rearrange themselves either releasing or absorbing energy in a process known as oxidation
How can a flame be sustained?
a chemical reaction must be able to maintain a rate of rapid oxidation that produces a self sustaining exothermic chemical chain reaction. this process will continue without the need for an additional external ignition source until all available fuel or oxidant is consumed, removed or the temperature reducing by cooling
When does combustion occur?
when heat does not dissipate faster than it is created
What are the objectives of combustion?
-complete destruction of organic matter to form harmless gasses
-prevention of the release of harmful materials into the atmosphere
What is the simplest combusion process?
fuel + oxygen = carbon dioxide + water
What is complete combustion?
The theoretical point where the ratio of fuel to oxygen results in this when all the carbon in the fuel forms CO2 and all the hydrogen forms H2O is called stoichiometric combustion (this is considered to be perfect combustion)
Why is it the goal of combustion processes to operate as closely as possible to stoichiometric combustion?
maximize efficiency and reduce emissions into the environment as the result of incomplete combustion
When does incomplete combustion occur?
when complete combustion of a combustible material doesnt happen. Lack of oxygen results in one atom of carbon uniting with only one atom of oxygen, creating carbon monoxide (CO) rather than carbon dioxide (CO2)
Why is it necessary to control the amounts of air to achieve complete combustion?
to ensure the burning of all fuel
What is excess air?
the amount of air necessary to make certain all energy is retrieved. Adjustment of the combustion process sos that the proper level of excess air is present is key
What do cremator operators make adjustments based on?
-type of fuel supply
-changes in atmospheric pressure
-time of day
How does combustion spread?
from the ignition source to the adjacent layer of gas mixture. In turn, each point of buring layer serves as ignition for the next one
When does combustion end?
When total heat energies of the reactants and the total heat energies of the products reach equilibrium. Reactants are the substances that take part in and undergo change during a chemical reaction
What is primary incineration?
Drying of combustible material to drive off moisture, volatilization of the vapors and gasses which occur as the temperature of the material rises, combustion of the charge and burnout of the solids.
What is secondary incineration?
Combustion of the vapors, gases and particulates driven off during the primary process
Crematory incinerators are defined as Class VI Crematory and pathological incinerators suitable for type 4 waste. What is type 4 waste?
Pathological. 100% human and animal tissue, organs and solid organize wastees from hospitals, laboratories, animal pounds, farms, abattoirs, etc. containing up to 85% moisture by weight. average heat value 1k-2k BTU/lb
What are some matierals that some states will not cremate?
-municipal solid waste
-Medical/infectious waste
-Radioactive waste
-Fiberglass and plastic
-Narcotics
What is a cremator?
Multichambered retort that is specificlaly designed for the incineration of human remains
Cremators have two basic multi chamber designs. What is the in line hearth?
combustion gases flow vertically
Cremators have two basic multiple chamber designs. What is a retort hearth?
-Flow of combustion gases is directed sideways through a secondary chamber adhacent to the primary combustion chamber
-the most efficient design for cases weighing less than 750 lbs.
What is the operation of a crematorium?
-placement of the case or charge into the primary combustion/incineration chamber
-closing and locking of the loading door
-ignition of the afterburner to bring the secondary chamber up to the target temperature
-ignition of the primary burner once target temperature is achieved
-the case is dried, ignited and combusted by the heat provided by the primary chamber burner as well as radiant heat from the refractory walls
-vaporization of moisture and volatile components which are then passed out of the primary chamber through a flame port
-excess air is added through the flame port and mixed with volatile contents in the secondary chamber, where they are ignited by a burner there
-gasses exit the secondary chamber through the cremator stack
-when all waste is driven off or consumed, the primary burner shuts off, followed by the afterburner after a set amount of time
-the chamber is allowed to cool and the cremated remains are removed
How does time affect the efficiency of a cremation?
it is essential that the products of combustion be given enough retention time in the afterburner chamber/primary cremation chamber to be consumed so they arent released into the atmosphere
How does temperature affect the efficiency of a cremation?
-proper temperature range is between 1.4k-1.8k f
-some states require the secondary chamber to remain at 1.8k during operations to ensure total incineration of the cremation container or any other products of combustion
-temperatures above 1.8k F will cause products of combustion to move through the afterchamber too quickly, resulting in visible emissions
How does turbulence affect the efficiency of a cremation?
-increases combustion efficiency
-created in the cremator’s exhaust system by having the gasses change directions through perforated walls and baffle systems
-Aids in the mixture of gases, driving off and consuming any products of combustion before release into the atmosphere
The average human body is between __ moisture
60-90%. For this reason, retorts are designed with a fixed hearth with a raised edge at the door to prevent liquids from spilling during charging
The average heat value as fired of a human body is ___ BTU/lb
800-3k
What are the major constituents of air emissions from cremation?
-organic compounds
-nitrogen oxides
-sulfur dioxides
-carbon monoxide
-particulate matter
What do emission rates depend on?
the design of the cremator, combustion temperatures, gas retention time, hot air duct design, stack temperature, and any control devices
What are particulate matter emissions?
-complex mixture of extremely small solid particulates and or water droplets
-composed of a number of components, including acids (nitrates and sulfates), organic chemicals, metals and soil or dust particles
-generated during the cremation process from incomplete fuel combustion of the charged remains
-effectively controlled by proper equipment design and operation
-measured as a concentration (grains per cubic feet of air)
What is the typically PM standard for crematories?
Cannot exceed 0.08 grains per dry standard cubic foot of flue gas
What is opacity (or exhaust smoke) an indicator of?
improper combustion and excessive particulate emissions. Opacity is the degree to which light is reduced when viewed through a smoke plume. Visible emissions are measured in percent opacity.
What does 0 percent opacity mean?
100% of the background is visible through the exhaust and vice versa
How can excess visible emissions be minimized?
constantly monitoring combustion temperature perameters
What are wet scrubbers?
an add on pollution control device that are used to trap suspended particles by direct contact with a spray of water or another liquid. Sometimes called flue gas washers. Washes fly ash, odorous compounds, and other objectionable materials out of the airstream as theyre carried along by droplets in the spray. Not commonly used in the US on cremation equipment thanks to the high costs.
What is a baghouse/fabric filtration?
An add on pollution control device that removes suspended particulates using an assembly of fabric filter bags. Dust laden air is blown upward by fans that trap the particulates inside. Offers high resistance to air flow, leading to substantial energy use to the system. Uncommon usage due to high costs.
