Smoke emissions coal-derived fuel

Synthetic liquid fuels derived from coal and shale will differ in some characteristics from conventional fuels derived from petroleum. For example, liquid synfuels are expected to contain significantly higher levels of aromatic hydrocarbons, especially for coal-derived fuels, and higher levels of bound nitrogen. These differences can affect the combustion system accepting such fuels in important ways. In continuous combustors, i.e. gas turbines, the increased aromatics content of coal-derived fuels is expected to promote the formation of soot which, in turn, will increase radiation to the combustor liner, raise liner temperature, and possibly result in shortened service life. Deposit formation and the emission of smoke are other potential effects which are cause for concern. Higher nitrogen levels in synfuels are expected to show up as increased emissions of N0X (NO+NO2) An earlier paper presented results of an experimental study on the effect of aromatics and combustor... 

Combustion tests of fuel oil blends derived from the Exxon Donor Solvent (EDS) process were carried out in a laboratory 50 hp test boiler and a commercial 1425 hp boiler. All tests showed that coal derived fuel oils burn cleanly compared to petroleum fuels with low levels of smoke and particulates. Emissions of N0X were related to fuel nitrogen content for both the petroleum and coal-derived fuels. 

This paper covers the combustion performance of EDS fuel oil blends, with primary emphasis on the emissions of polynuclear aromatics (PNA). Previous testing of EDS fuel oil blends 0, 2) and other coal derived fuel oil blends (2) has shown that emissions of particulate and smoke are lower with coal-derived fuel oils than from the combustion of petroleum-derived fuel oils. 

The emission measurements during this testing included N0X, smoke, particulate and PNA. N0X was determined by a non-disper-sive infrared analyzer, and smoke by the Bacharach test. Both the particulates and PNA were sampled by a source assessment sampling system (SASS). The SASS system isokinetically samples a fraction of the stack gas and traps particulates in a series of cyclones, which classify the particulate by size. Final filtration is through a fiberglass filter mounted in an oven heated to 200°C to prevent condensation of acids. In this program, the cyclones were not used, since previous work (3) had shown the particulate from coal-derived fuel oils to be small, with an average diameter on the order of 0.4 /um. The PNA which is not deposited on the particulate is collected on XAD-2 resin after the gas has been cooled to 15-20°C. PNA analyses were carried out on a combined extract from the particulate, XAD-2 resin, other condensates in the system, and the solvent rinses used to clean the SASS system. 

Results of these tests are shown in Table IV. The average emissions values are shown for the coal-derived fuels. As previous testing has shown, the EDS fuel oils produced little particulate relative to the petroleum fuel, while the smoke values for the coal-derived materials were equal to or less than that of the RSFO. As with the laboratory testing, the N0X level was a function of the fuel nitrogen level, although N0X emissions from the commercial unit were lower than from the laboratory boiler. 

Nitro-PAHs are polycyclic aromatic hydrocarbon derivatives that contain one or more nitro groups covalently bound at chemically reactive positions on the aromatic ring. Mixtures of nitrated PAHs are generated either by reactions of PAHs with nitrogen oxides or as byproducts of the incomplete combustion of fossil fuels (65). A wide variety of nitro-PAHs have been isolated from environmental sources, such as coal fly ash, diesel emission particulates, cigarette smoke and carbon black photocopier toners (29, 52, 63, 74, 75, 86, 87, 88). Structures of representative nitro-PAHs isolated from the environment are shown in Figure 1. 

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