MDI Emissions Reporting Guidelines for the ... - Polyurethanes

MDI Emissions Reporting Guidelines for the Polyurethanes Industry
13. Oriented Strand Board (OSB)
Methylenebis (phenyl isocyanate) (MDI) is used as a binder in the production of
particleboard. The process consists of four steps:
Step I: Wood chips, straw, wheat, hays, or other grains are grounded up and
conveyed into moisturizing chamber. Water is either added or removed to a specific
moisture content.
Step II: The mixture of woodchips and water is transferred into second chamber
where MDI is added to a specific weight equivalent. Chamber is a closed system with
no vent.
Step III: The combination of wood, water and MDI is mixed and then spread over a
"cold plate" frame that forms an 8-inch matting. The “cold plate” moves along a
conveyor system where 5-6 frames are loaded onto a press where a hydraulic system
compresses the mixture to a desired thickness between 1/4" to 5/8", the "cold plate"
is heated to a design temperature. During this step the MDI reacts with the water to
form a polyurethane bond with the fiber. The press is open and the trapped carbon
dioxide is released. The press is equipped with a blower system that vents to the
roof. The press blower is also used to exhaust the air from other parts of the process.
Step IV: The formed boards are removed from the press, checked for quality,
trimmed to the designed length and width.
The controlling parameters that influence the emission rate are the temperature, flow rate
and concentration of the exit gas stream. The worst-case scenario is that the exit gas
stream is saturated with MDI.
The estimated MDI emission can be calculated using the following formula:
L = (V air /359) * (273.15/T sp ) * 60 * (C mdi /1000000) * M W * k MDI * C f
Where:
L = the emissions in lb/hr
Vair = the exhaust airflow rate in ft3 /min
Tsp = the exhaust temperature in K
Cmdi = the MDI concentration, in ppmv, in the exhaust air
MW = the molecular weight of MDI (250.26)
KMDI = the adjustment factor to the vapor pressure that is a function of MDI
concentration in the feedstock and the temperature.
Cf = per cent MDI/PMDI in solution
359 = the molar volume of an ideal gas in ft3 /lb-mole @ 0 o
C and 1-atmosphere.
C mdi = (VP MDI /760) x 10 6
VP MDI = MDI vapor pressure at exhaust temperature
D-12