OCR Text |
Show exists for the required concentration of reducing agents. Operating the engine extremely fuel rich imposes a fuel penalty. Major environmental concerns with N S C R systems are associated with ammonia, C O and T U H C emissions and with the disposal of spent catalyst modules. Although NSCELsystems dojiot inject ainmonia, as do S P R systejris, ammonia levels between 10 and 160 p p m have been measured. CO~ancfTUHC at the engine outlet increase, however, across the N S C R catalyst major air toxic organic compounds are reduced along with these NO,, C O , and T U H C . Table 10 lists recent test data obtained on a 650 bhp Dresser -Rand pipeline engine retrofitted with NSCR. All major emissions were reduced across the catalyst including ppb levels of benzene, toluene, and formaldehyde. -/ Field Adjustments and Minor Equipment Modifications In addition to clean-burn retrofit kits and SCR, there are other candidate controls for 2- and 4-stroke lean combustion engines that entail minor field adjustments and equipment modifications or upgrades. These options are listed in Table 11. These control approaches have N O x reduction efficiencies in the range of 10 to 50 percent, depending on the adjustments and equipment modifications and the type of engine, i.e., existing air charging method and efficiency. In addition to efficiency losses these controls often increase emissions of C O and T U H C because of lower peak cylinder temperatures and less than optimum ignition timing. Table 10. Emission test results from a NSCR-equipped 650 bhp LV6-8 rich-burn engine" \> scfff> XJ ? > ^ s i/ NOx CO T U HC Benzene Toluene Formaldehyde N S C R Inlet 550 bhp 610 1,250 230 0.21 0.056 NM 650 bhp 680 1,100 110 0.14 0.037 0.0072 N S C R Outlet 550 bhp 51 610 100 0.017 < 0.005 NM 650 bhp 7 260 83 0.017 < 0.005 0.0007 Percent Change 550 bhp -92 -51 -57 -92 -91 - 650 bhp -99 -76 -25 -88 -86 -90 a- All emissions are reported in p p m @ 15 percent 0 2 Source: Reference 5 6.0 C O N C L U S I O NS Control of existing gas turbine at pipeline compressor stations is not feasible with the use of W I or SCR. Significant technical and economic challenges exists because of the remoteness of these engines, their relatively unattended operation and variable load duty cycles, and because the cost of increased maintenance and supervision. D L N C , once fully developed and demonstrated by 11 1-4 |