Dual fuel

LPG, stored as a liquid at its saturation pressure, is vaporized and introduced as vapor in conventional spark ignition motors. These motors are not modified with the exception of their feed system. Moreover, in the majority of cases, dual fuel capabilities have been adapted, that is, the vehicle can use either LPG or liquid fuel. 

Methanol, a clean burning fuel relative to conventional industrial fuels other than natural gas, can be used advantageously in stationary turbines and boilers because of its low flame luminosity and combustion temperature. Low NO emissions and virtually no sulfur or particulate emissions have been observed (83). Methanol is also considered for dual fuel (methanol plus oil or natural gas) combustion power boilers (84) as well as to fuel gas turbines in combined methanol / electric power production plants using coal gasification (85) (see Power generation). 

A. J. Weir and co-workers, "Methanol Dual-Fuel Combustion," paper presented at 1987Joint Symposium on Stationay Combustion MO Control, New Odeans, La., Mar. 23—26, 1987. 

Injection of Steam in the Combustor of the Gas Turbines Utilizing Present Dual Fuel Nozzles. Steam injection in the combustor has been commonly used for NO control as seen in Figure 2-43. The amount of steam, which can be added, is limited due to combustion concerns. This is limited to about 2-3% of the airflow. This would provide an additional 3-5% of the rated power. The dual fuel nozzles on many of the industrial turbines could easily be retrofitted to achieve the goal of steam injection. The steam would be produced using an HRSG. Multiple turbines could also be tied into one HRSG. 

Finally, fuel availability must be considered. If future reserves are unknown, or seasonal variations are expected, dual fuel capability must be considered. 

The gas turbines major limitations on the life are the eombustor eans, first stage turbine nozzles and first stage turbine blades as seen in Figure 21-6. The effeet of dry Low NO eombustors have been very negative on the availability of Combined Cyele Power Plants, espeeially those with dual fuel eapability. Flash baek problems are a very major problem as they tend to ereate burning in the pre-mix seetion of the eombustor, and eause failure of the pre-mix tubes. These pre-mix tubes are also very suseeptible to resonanee vibrations. 

Prime movers are typically fueled by natural gas or diesel. Dual fuel turbine units exist that can run on natural gas and can automatically switch to diesel. So-called dual fuel reciprocating engines run on a mixture of diesel and natural gas. When natural gas is not available, they can automatically switch to 100% diesel. Most prime movers associated with producing facilities are typically natural gas fueled due to the ready availability of fuel. Diesel fueled machines are typically used to provide stand-by power or power for intermittent or emergency users such as cranes, stand-by generators, firewater pumps, etc. 

Power unit manufacture also produce diesel engines that can be converted to operate on a dual fuel carburation of about 10% diesel and natural gas. Such conversions are more difficult than converting spark-ignition engines to various gas fuels. 

Performance on gas is normally limited in dual-fuel applications to that of the oil burner. In gas-only... 

Oil burners Type Size range Dual-fuel capability Fuel type Atomizing Atomizing pressure viscosity (bar) (cS) Turndown ratio Flame characteristics Main applications... 

Gas burners Type Size Dual-fuel Fuel type Gas pressure Turndown ratio Flame Characteris tics Main applications... 

Nozzle mix 30kW-40MW Yes All gases 15 mbar-1.5 mbar <20 1 depends on oil turndown when dual-fuel Normally nonluminous shape depends on burner and register configuration Wide use in packaged burners of all sizes. Common in hot water and steam boilers of all sizes... 

This is very common nowadays to allow bargaining on fuel price or to arrange an interruptible gas tariff, which is backed up at times of peak demand with a stored oil supply. Most types of oil and gas burner are available in dual-fuel form, normally with gas burner design wrapped around the arrangement for oil firing. This is usually the more difficult fuel to burn, particularly in the case of residual heavy oils. Fuel selection is normally by a switch on the burner control panel after isolation has taken place of the non-fired fuel. To avoid the cost and complexity of the fuel preheating on oil firing, smaller systems use gas oil as the standby fuel. 

Fluid beds can be fired with gas and oil across the top of the slumped bed since sufficient freeboard exists with coal firing to prevent particle elutriation. Oil, gas or dual-fuel burners so arranged could also provide the means for bed preheating, especially if the flame is redirected down to the fluidization zone. 

Gas turbines operate on natural gas, synthetic gas, landfill gas, and fuel oils. Plants are often designed to operate on gaseous fuel with a stored liquid fuel for backup, so as to obtain the less-expensive interruptible rate for natural gas. Dual fuel combustion capability is a purchase option on many gas turbines. The turbine is ideally suited as an integral component in the IGCC train. Further, modern gas turbines have proven to be reliable power generators, given proper maintenance. Time to overhaul is typically 25,000 to 50,000... 

The United States passed the Energy Policy Act in 1992. One goal was to reduce the amount of petroleum used for transportation by promoting the use of alternative fuels in cars and light trucks. These fuels included natural gas, methanol, ethanol, propane, electricity, and biodiesel. Alternative fuel vehicles (AFVs) can operate on these fuels and many are dual fueled also running on gasoline. 

Significant improvement of the combus-tion energy release was obtained by introduc-ing a dual-fuel injection scheme. Fuel is in-P jected twice per air vortex shedding. Fig-... 

Figure 6.12 Planar images of the air and fuel mixing pattern and reaction zone imaged by OH fluorescence of the ethylene flame at low-soot conditions and dual-fuel injection at the first (a) and second (6) injection time...

An additional benefit of this configuration was the ability of all drivers to be dual-fueled for start-up assistance or automatic switchover if gas pressure failed. 

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