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Show from $1,700 to $4,400 per ton of N O x reduced. Emissions of C O and total unburned hydrocarbon ( T U H C ) increase with the retrofit of these clean-burn kits. Li) P $t -h /p\j$-J Prestratified Charge (PSC) for Uncontrolled Rich-Burn Reciprocating Engines PSC technology, developed at Cornell University in the mid 1970s, is a combustion modification that enables rich-burn engines to operate with a lean A / F mixture. In the control, additional air is added after the carburetor to produce a lean mixture. Before a fresh charge, or A / F mixture, is introduced in the cylinder, it is prestratified, "prearranged" in the ports and runners by dilution straws. Essentially, the standard mixture is forced behind an extremely lean A /F mixture. The rich standard mixture provides the "pilot flame" for ignition stability of the much leaner mixture. PSC systems have been retrofitted on small (less than 1,500 bhp) natural gas prime movers. Unlike clean-burn retrofit kits for uncontrolled lean-burn engines, which entail the modification and replacement of many components, P S C retrofit control systems are relatively simple, consisting of only a new intake manifold and air control system, i.e., an air filter and dilution system. P S C allows a rich-burn engine to operate with a lean A / F mixture. PSC systems routinely achieve an 80 percent, and in most cases, a 90 percent NOx reduction performance compared to baseline emissions, emitting a controlled N O x level of 2 g/hp-hr or less. This N O x reduction benefit is somewhat offset by increases in both C O and T U H C emissions as illustrated by a typical retrofit data shown in Table 9. The cost effectiveness of P S C retrofit on existing rich-burn engines is estimated to range between $470 and $1,170 per ton of N O x reduced. Table 9. Emission characteristics of a rich-burn engine retrofitted with P S C Emission Parameters NOx CO TUHC Uncontrolled Pre-retrofit 1,485 113 477 PSC-Controlled Post-retrofit 156 211 2,218 Percent Change -89 + 87 +365 a - All data are in p p m dry corrected to 15 percent Oz. Source: Reference 4 Nonselective Catalytic Reduction (NSCR) for Rich-Burn Reciprocating Engines MX _ r N S C R control technology has been in use since the late 1970s, but was not considered fully demonstrated for rich-burn engines until the late 1980s. A survey conducted in 1986 found that approximately 1,000 N S C R systems were in operation, some on pipeline rich-burn engines. By careful control of the exhaust gas composition and temperature, through control of the A / F ratio, the C O and T U H C will reduce N O x to N * in the presence of a catalyst. A narrow operating band 10 1-4 |