Control of Volatile Organic Compounds Emissions from Manufacturing

analysis of the Distil 1 ation NSPS.~~Ducti ng costs were calculated
based on the installed cost equations given in the GARD Manual .I8
Installed costs were put on a June 1980 basis using the following
Chemical Engineering PI ant Cost Indices: the overall index for thermal
incinerators; the pipes, valves, and fittings index for piping; and the
fabricated equipment index for ducts, fans, and stacks. Annualized
costs were calculated using the factors in Table 5-3. The electricity
required was calculated assuming a 6-inch Hz0 pressure drop across the
system and a blower efficiency of 60 percent.
5.1.2 Flare Design and Cost Basis
Elevated steam-assisted flares were costed based upon 60 fps and
300 Btu/scf and standard design techniques. Associated piping and
ducting from the process sources to a header and from a header to the
flare were conservatively designed for costing purposes. Operating
costs for utilities were based on industry practice.
5.1.2.1 Flare Design. Design of flare systems for the combinations
of waste streams was based on standard flare design equations for diameter
and height presented by IT ~nvi roscience.lg These equations were simp1ified
to functions of the following waste gas characteristics: volumetric
flow rate, lower heating value, temperature, and molecular weight. A
minimum commercially available diameter of 2 inches was assumed. The
height correlation premise is design of a flare that will not generate a
lethal radiative heat level (1500 ~tulft2 hr, including solar radi ationzo)
at the base of the flare (considering the effect of wind). Heights in
5-foot multiples with a minimum of 30 ft. were used.21
Supplemental fuel , natural gas, is added to increase the heating
value to 300 Btu/scf to help ensure 98 percent VOC destruction, For
flares with diameters of 24-inches or less, this natural gas was assumed
to be premixed with the waste gas and to exit out the stack. For larger
flares, a gas ring at the flare tip was assumed because such separate
piping is more economical than increasing the flare stack size for 1 arge
diameter.
Purge gas also may be required to prevent air intrusion and
flashback. A purge velocity requirement of 1 fps was assumed during