LOW EMISSION

Similar to the fullerene ground state the singlet and triplet excited state properties of the carbon network are best discussed with respect to the tliree-dimensional symmetry. SurjDrisingly, the singlet excited state gives rise to a low emission fluorescence quantum yield of 1.0 x 10 [143]. Despite the highly constrained carbon network,... 

Future technology developments in paraffin alkylation will be greatly influenced by environmental considerations. The demand for alkylate product will continue to increase because alkylate is one of the most desirable components in modern low emission gasoline formulations. Increased attention will be focused on improving process safety, reducing waste disposal requirements, and limiting the environmental consequences of any process emissions. 

Sputtered silver mirrors are used for solar energy (qv) collectors and astronomical telescope mirrors. Approximately 3 t/yr of silver are used in the United States for low emissivity windows. 

Black and colored plates can also be obtained from chromic acid baths. The plates are mostly oxides (177). Black chromium plating bath compositions are proprietary, but most do not contain sulfate. The deposit has been considered for use in solar panels because of its high absorptivity and low emissivity (175). 

Emission Control Technologies. The California low emission vehicle (LEV) standards has spawned iavestigations iato new technologies and methods for further reducing automobile exhaust emissions. The target is to reduce emissions, especially HC emissions, which occur during the two minutes after a vehicle has been started (53). It is estimated that 70 to 80% of nonmethane HCs that escape conversion by the catalytic converter do so during this time before the catalyst is fully functional. 

Radiation differs from conduction and convection not only in mathematical structure but in its much higher sensitivity to temperature. It is of dominating importance in furnaces because of their temperature, and in ciyogenic insulation because of the vacuum existing between particles. The temperature at which it accounts for roughly half of the total heat loss from a surface in air depends on such factors as surface emissivity and the convection coefficient. For pipes in free convection, this is room temperature for fine wires of low emissivity it is above red heat. Gases at combustion-chamber temperatures lose more than 90 percent of their energy by radiation from the carbon dioxide, water vapor, and particulate matter. 

The insertion of low-emissivity floating shields within the evacuated space can effectively reduce the heat transport by radiation. The effect of the shields is to greatly reduce the emissivity factor. For example, for N shields or N + 2) surfaces, an emissivity of the outer and inner surface of and an emissivity of the shields of the emissivity factor reduces to... 

In essence, one properly located low-emissivity shield can reduce the radiant heat transfer to around one-half of the rate without the shield, two shields can reduce this to around one-fourth of the rate without the shield, and so on. 

Find low-emission ]. Be knowledgeable 1. Adopt test 1. Adopt ventilation I. Adopt indoor air 1. Conduct studies of 1. Conduct research... 

An external combustion engine that has been widely supported as a low-emission power source is the Rankine cycle steam engine. Many different types of expanders can be used to convert the energy in the working fluid... 

Fuel cells, which rely on electrochemical generation of electric power, could be used for nonpolluting sources of power for motor vehicles. Since fuel cells are not heat engines, they offer the potential for extremely low emissions with a higher thermal effidency than internal combustion engines. Their lack of adoption by mobile systems has been due to their cost, large size, weight, lack of operational flexibility, and poor transient response. It has been stated that these problems could keep fuel cells from the mass-produced automobile market until after the year 2010 (5). 

Although water injection is still used, dry control combustion technology has become the preferred method for the major players in the industrial power generation market. DLN (Dry Low NOx) was the first acronym to be coined, but with the requirement to control NOx without increasing carbon monoxide and unburned hydrocarbons this has now become DLL (Dry Low Emissions). 

The gas turbine eombustors have seen eonsiderable ehange in their design as most new turbines have progressed to Dry Low Emission NOx Combustors from the wet eombustors, whieh were injeeted by steam in the primary zone of the eombustor. The DLE approaeh is to burn most (at least 75%) of the fuel at eool, fuel-lean eonditions to avoid any signifieant produetion of NOx. The prineipal features of sueh a eombustion system is the premixing of... 

Figure 10-23 shows a sehematie eomparison of a typieal dry low emission NOx eombustor and eonventional eombustors. In both eases, a swirler is used to ereate the required flow eonditions in the eombustion ehamber to stabilize the flame. The DLE fuel injeetor is mueh larger beeause it eontains the fuel/air premixing ehamber and the quantity of air being mixed is large, approximately 50-60% of the eombustion air flow. 

Figure 10-23. A sohematio oomparison of a typioal dry low emission NOx oombustor and a oonventional oombustors.

Figure 10-24. Schematic of a dry low emission NOx combustor (Courtesy ALSTOM.)...

Figure 10-24 shows a schematic of an actual dry low emission NO combustor used by ALSTOM in their large turbines. With the flame temperature being much closer to the lean limit than in a conventional combustion system, some action has to be taken when the engine load is reduced to prevent flame out. If no action were taken flame-out would occur since the mixture strength would become too lean to burn. 

Figure 10-25. Shows the staging of dry low emissions combustor as the turbine is brought to full power.

Dalla Betta, Ralph A., Nicholas, S.G., Weakley, C.K., Lundberg, K., Caron, T.J., Chamberlain, J., and Greeb, K., Field Test of a 1.5 MW Industrial Gas Turbine with a Low Emissions Catalytic Combustion System, ASME 99-GT-295. 

Dutta, P., Cowell, L.H., Yee, D.K., and Dalla Betta, R.A., Design and Evaluation of a Single-Can Full Scale Catalytic Combustion System for Ultra-Low Emissions Industrial Gas Turbines, ASME 97-GT-292. 

Greenwood, S.A., Low Emission Combustion Technology for Stationary Gas Turbine Engines, Proceedings of the 29th Turbomachinery Symposium, September 2000. 

Chiesa, P. and Consonni. S. (1999), Shift reaction and physical absorption for low emission IGCCs, ASME J. Engng Gas Turbines Power 121(2), 295-305. 

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