Fuel preheating

With heavy fuels, the ambient temperature and the fuel type must be considered. Even at warm environmental temperatures, the high viscosity of the residual could require fuel preheating or blending. If the unit is planned for operation in extremely cold regions, the heavier distillates could become too viscous. Fuel system requirements limit viscosity to 20 centi-stokes at the fuel nozzles. 

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. 

The fuel cell Rankine cycle arrangement has been selected so that all fuel preheating and reforming are carried out external to the cell and air preheating is accomplished by mixing with recycled depleted air. The air feed flow is adjusted so that no heat transfer is required in the cell or from the recycled air. Consequently, the internal fuel cell structure is greatly simplified, and the requirement for a heat exchanger in the recycle air stream is eliminated. 

Tests were conducted using a scramjet combustor and the hypersonic facility of MAI equipped with kerosene-fueled preheater (vitiated air). Oxygen mass fraction T°02 in the vitiated air was slightly lower than in the atmospheric air. y°02 values for each test run can be found in Table 23.1. With an oxygen mass fraction in atmospheric air of 0.232, the kerosene equivalence ratio (ER) in vitiated air is determined by the following relation ... 

The highest quality spray for comparable atomizer conditions was obtained with the No. 2 fuel oil followed by SRC-II middle distillate and the No. 6 residual fuel (preheated up to 240°F). 

The boiler is equipped with a package burner that includes the following an adjustable fuel preheater to permit combustion of No. 6 oil, a fuel/air proportioning controller, an atomizing air supply, and a combustion air blower. 

To date, the test program has consisted of two periods of No. 6 fuel oil firing, two periods of SRC-II firing, and two combustion runs on No. 2 oil. Each test period was preceded by a few brief tests to shake down the boiler and determine settings for the atomizing air flow, fuel preheat temperature, and fuel/air proportioning controller. To date, eight runs have been made with No. 6 oil five at about 23% excess air and three at about 11 excess air. Two runs have been completed on No. 2 oil one at 11% excess air and one at 20% excess air. Five SRC-II fuels have been tested a... 

Heating Value Moisture Content Ash Content Excess Air Air Fuel Preheat... 

Most heat recovery efforts are aimed at utilizing the waste heat exiting through the flues. Some forms of heat recovery are air preheating, fuel preheating, load preheating (Fig. 1.17), recuperative, regenerative, and waste heat boilers—all discussed in chapter 5. 

Thermal management Fuel preheater, reformate preheater, recuperator, startup combustor, SOFC tailgas combustor, startup steam generator... 

Fuel preheat and vaporization. Necessary to prepare the fuel to meet the reformer s feed requirements. Often, this unit operation is physically integrated with the reformer. 

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