The National Fire Protection Association (NFPA) and FM Global both deal with the safety issues involved with industrial technologies like thermal oxidizers manufactured at NESTEC.
“The safety of our employees is the highest concern of the management of NESTEC, Inc. No job is so important or urgent that we cannot take the time to work safely.”
-Jim Nester, President, Nestec
The 2015 edition of NFPA 86 includes several changes to Chapter 3 due to the addition of definitions for burner management system, flame failure response time, flame detector, hardwired, combustion safeguard, and pressure regulator types.
NFPA 86, the National Fire Protection Association’s Standard for the Safe Operation of Ovens and Furnaces, and FM Global Property Loss Prevention Data Sheets 6-11 2.2.4.3, both address direct-fired thermal oxidizers as Class A Furnaces mandating the use of continuous Flammability Analyzers on inlet streams exceeding 25% LEL.
“Thermal oxidizer includes the following:
- Afterburner (Direct Thermal Oxidizer) is a direct thermal oxidizer, installed in series and downstream of process equipment, that generates VOC or HC; also, referred to as secondary combustion chamber.
- Direct Thermal Oxidizer is a combustion system in which the burner(s) directly heats VOCs or HCs to the destruction temperature without heat recovery to the incoming gases.
- Direct Catalytic Oxidizer is a combustion system in which the burner(s) directly heats volatile organic compounds (VOCs) or hydrocarbons (HCs) to the destruction temperature, prior to their introduction to a destruction catalyst, without heat recovery to the incoming gases, and in which the catalytic destruction temperature is lower than the non-catalytic (direct thermal) destruction temperature.
- Fume incinerators
- Recuperative Thermal Oxidizer is a combustion device in which the burner(s) directly heats VOCs or HCs to the destruction temperature and in which the hot products of combustion are used to indirectly heat the incoming gas stream before it contacts the burner flame.
- Recuperative Catalytic Oxidizer is a combustion system in which the burner(s) directly heats VOCs or HCs to the catalytic destruction temperature prior to their introduction to a destruction catalyst, after which products of combustion are used to indirectly heat the incoming gas stream before it contacts the burner flame, and in which the catalytic destruction temperature is lower than the non-catalytic (direct thermal) destruction temperature.
- Regenerative Thermal Oxidizer is a combustion device in which the burner(s) directly heats VOCs or HCs after the gas stream is preheated to the destruction temperature by the periodic flow reversal of the gas stream through heat storage media that alternately have been heated by the product gases during an exhaust cycle and then have given up their heat to the incoming reactant gases during an inlet cycle.
- Regenerative Catalytic Oxidizer (RCO) is a combustion system in which the burner(s) directly heats VOCs or HCs after the gas stream is preheated to the destruction temperature by the periodic flow reversal of the gas stream through beds of ceramic heat recovery media with a coating or layer of catalyst that alternately have been heated by the product gases during an exhaust cycle and then have given up their heat to the incoming reactant gases during an inlet cycle.
- Flameless Thermal Oxidizer is a direct recuperative or regenerative combustion system in which the burner(s) preheats the heat storage media prior to the introduction of VOCs or HCs and in which, subsequently; the destruction is carried out in interstices of the heat storage media in a flameless self-sustaining manner.”
-NFPA® Standard for Ovens and Furnaces 86
“The safety of our employees is the highest concern of the management of NESTEC, Inc. No job is so important or urgent that we cannot take the time to work safely.”
-Jim Nester, President, Nestec
“FM Global Property Loss Prevention Data Sheets 6-11
2.2.4.3 Use continuous combustibles analyzers if normal operation will exceed 25% of the LEL (LFL). Analyzers should alarm upon loss of signal or power. Flammable vapor concentration up to 50% of the LEL may be tolerated if continuous combustibles analyzers are used and property maintained, provided:
- The controller is arranged to:
- Sound an alarm before the concentration reaches 50 of the LEL.
- Shut down the fume source and process burners when the concentration reaches 50 of the LEL.
- Divert the fumes to a safe location out-of-doors when the concentration reaches 50 of the LEL, if permitted by local environmental regulations.
- Use positive seating, fast-acting slide gates or dampers for isolation.
- The entire combustibles sampling system, including the analyzer, is maintained at temperatures equal to or above the flash point of the least volatile component of the sampled mixture. This will prevent condensation, fouling and inaccurate readings. Flash point is a well-defined property. The dew point will normally, fall below this temperature at concentrations less than 50% of the LEL.”
-©2004 Factory Mutual Insurance Company
The fuel value of combustible vapors present in the air stream, flowing through the thermal oxidizer or incinerator, will provide an energy release which reduces the consumption of the primary fuel source, (natural gas or other). A Regenerative Thermal Oxidizer (RTO) becomes self- sustaining, (virtually no fuel consumption) with combustible vapor streams at approximately 2.4 to 3% LEL. While the added fuel value of many combustible vapors reduces the oxidizer’s use of natural gas, it can also present a risk of explosion, if the concentration rises too high.
The inlet streams for many oxidizers contain a mixture of combustible vapor in differing proportions and concentrations. Oxidizers used for exhaust gas combustible vapor destruction often process streams of unknown content. In either instance, it is essential for safe operation to accurately calculate the LEL (LFL) and/or use an analyzer capable of measuring the true flammability of the mixed vapors. The estimated LEL (LFL) for a mixture of combustible vapor (VOC, HAP, CO, or other) can be calculated with the LeChatelier’s rule (Kuchta, 1985; LeChatelier, 1891) or Group method (AIChE 1994).
ESTIMATING LEL (LFL) – LeChatelier method
MLFL (LEL) = 100 / S( Ci /LFL i (LEL i))
- MLFL: the mixture lower flammability limit (vol %)
- Ci: the concentration of component I in the gas mixture on an air free basis (vol %)
- LFL (LEL): the lower flammability limit for compound I in the mixture (vol%)
- For equimolar mixtures, all valves of Ci are equal to 100/N
- N: the total number of components (other than air)
- Carbon tetrachloride (CT), 1/LFT ct is taken as 0 as an inert diluent
ESTIMATING LEL (LFL) – Group method (AIChE 1994)
MLFL (LEL) = 100 / S( fiGCFi )
- MLFL: the mixture lower flammability limit (vol %)
- fi: the mole or volume fraction of gas I in the mixture on an air free basis
- GCFi: the group contribution factor for a compound i
- GCFi =S (njGFj)
- nj: the number of group type j in compound i
- CFi: the group factor for group type j
NESTEC maintains a 1,300+ chemical VOC, HAP, CO and other hydrocarbon list as well as a program to establish the approximate LEL (LFL) on all applications, which is then evaluated to establish the required potential oxidizer/concentrator equipment. The level of LEL (LFL) will help to determine the thermal energy recovery (TER) required for the oxidizer to minimize or eliminate any auxiliary fuel consumption.
If you have a potential process change and/or new process exhaust that requires air emission control, contact NESTEC for a free process analysis.
For assistance from our extensive experience, call or e-mail NESTEC Inc. for a free evaluation of your air emission control equipment needs.
Office: 610.323.7670
Jim Nester, CEO: jnester@nestecinc.com
Rick Reimlinger, Vice President: rick.reimlinger@nestecinc.com
Rodney L Pennington, PE, Vice President of Key Accounts: rpennington@nestecinc.com
William Holden, Services Manager: jredcay@nestecinc.com
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