MDI Emissions Reporting Guidelines for the ... - Polyurethanes

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Therefore: MDI Emissions Reporting Guidelines for the Polyurethanes Industry Cmdi = (VPMDI /760) x 10 6 VPMDI = MDI vapor pressure at exhaust temperature RMDI = unreacted fraction of MDI L = the emissions in lb/hr Vair = 8500 ft3 /min Tsp = 250 o F = 394.2 K MW = 250.26 KMDI = .69 Cf = 15% 359 = the molar volume of an ideal gas in ft 3 /lb-mole @ 0 o C and 1-atmosphere VP MDI = 0.08788 mm C mdi = (0.08788/760) x 10 6 = 115.6 ppmv R MDI = 1.0 L = (V air /359) * (273.15/T sp ) * 60 * (C mdi /1000000) * M W * k MDI * C f L = (8500/359)*(273.15/394.2)*(115.6/1000000)*(250.26)*(.69)*(.15)*(60)*(1) L = 2.94 lbs/hr (Worst case: No reaction/No control) If the amount of excess of MDI present in the vat solution is known, then this can be factored into the equation. However, based upon the above set of conditions the maximum emission rate cannot exceed 2.94 lbs/hr. 7.0 Boardstock (Open Process) Releases of MDI will be calculated for a laminate boardstock manufacturing facility that uses 1,300,000 pounds of MDI-based component of a rigid foam system each year. MDI/PMDI component is shipped to the facility in tank trucks and is transferred to a 5,000-gallon indoor storage tank that is temperature controlled. The MDI component product is transferred to 2,000 pound capacity “day tanks” which are stored inside the producing facility. Both the storage tanks and day tanks are kept at a constant temperature of 77 o F (25 o C). The contents of the “day tanks” are pumped through a metered foam machine and then delivered, mixed with the polyol, additives, blowing agent and other ingredients of the rigid foam system, and applied to the bottom facer of the moving laminate conveyor line. The laminate conveyor passes through a heated oven where the temperature is kept at a constant 180 o F. The tack-free time is 5 seconds. Assume that the hot air in the oven passes over the laminate surface once at a rate of 5 meters/second. The facility produces laminate boardstock that is on average 2 inch thick by 4 feet wide at the rate of 10 linear feet per minute. The operation takes place in an area that measures 150 feet long x 25 feet wide x 20 high (100,000 ft. 3 ). The air concentration in the workplace shows 0.001 ppm MDI. The building under goes 5 air changes per 5-17
MDI Emissions Reporting Guidelines for the Polyurethanes Industry hour, and production operates 16 hours per day 250 days a year. Calculating Stack Emissions To estimate emissions from open processes such as boardstock production, it is assumed that MDI will migrate from all exposed surfaces. The evaporation losses are a function of the process temperature, the airflow speed in the vicinity of the process, the tack-free time and the exposed surface area. The calculation methodology involves four steps: 1. Determine partial pressure of MDI at tack-free time. 2. Determine exposed area. 3. Determine evaporation rate. 4. Apply adjustment factor. The evaporation rate (in gram/day) is determined from the following expression: Where: W = 25.4 * VP mdi * (M w / T proc ) * (u) 0.78 * S A * t TF * K mdi W = the evaporation losses from the open process in gram/day VPmdi = the vapor pressure of MDI in atm. at process temperature Tproc = the process temperature in K. This is the maximum temperature of the MDI tackfree time Mw = 250.26 (this is the molecular weight of MDI) U = the airflow speed in m/sec. This is the airflow in the vicinity of the process SA = the exposed surface area in M2 . This is the exposed surface area per day. For boardstock production, the surface area can be determined from the dimensions of the board tTF = the tack-free time in seconds. The default value is 5 sec Kmdi = the adjustment factor to the vapor pressure that is a function of MDI concentration in the feedstock and the temperature The open process losses are determined by multiplying the evaporation losses per day by the number of days the process is in operation. Step I: Determine Total Exposed Area The total exposed surface area (SA ) will be the total exposed surface area of foam that is generated each day, including the area of foam that is exposed when the foam is cut at the end of the conveyor line. The foam is substantially cured when it is cut into slabs at the end of the conveyor line. 5-18
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700 2nd Street NE • Washington, D
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