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At higher concentrations of vanadium， magnesium sulfate or magnesiumoxide is used as an inhibitor. Both are approximately equal in materialcost，but magnesium sulfate has proven itself， while magnesium oxide is still understudy. Magnesium sulfate requires by far the most capitalcost， as it must befirst dissolved， then adjusted to a known concentration. It is mixed with an oil and an emulsifying agent to form an emulsion to suspend in the fuel. Two different injection procedures are used. One method is to mix the solution with desalted fuel in a dispersion mixer just prior to the combustion chamber.The inhibited oil is burned quickly， usually within a minute aftermixing，because the solution has a tendency to settle out.Also， the solution can be dispersed in the fuel prior to the service tanks. To avoid settling out of thesolution， the tanks are recirculated through distribution headers. Since a magnesium-to-vanadium ratio of 3.25 . 0.25 :1 is used in practice， the second dispersion method is the standard practice as the tanks can be certified ""within specification"" before burning. Adequate knowledge of contaminants is essential for successful inhibition.
An alternate approach to fuel washing is to utilize a vaporized fuel oil system (VFO). This technology was developed as a method for converting natural gas fuel systems to liquid fuel. The process involves mixing steam with the liquid fuel and then vaporizing the mixture. The vaporized mixture exhibits the same combustion properties as natural gas.
VFO works well in gas turbines. In a nine-month testprogram， the combustion properties of VFO were studied in a combustion test module. A gas turbine was also operated on VFO. The tests were conducted to studythe combustion characteristics of VFO， the erosive and corrosive effects ofVFO， and the operation of a gas turbine on VFO. The combustion tests were conducted on a combustion test module built from a GE Frame 5 combus-tion can and liner. The gas turbine tests were conducted on a Ford model 707 industrial gas turbine. Both the combustion module and gas turbine were used in the erosion and corrosion evaluation. The combustion testsshowed the VFO to match natural gas in flame patterns， temperature profile， and flame color. The operation of the gas turbine revealed that the gasturbine not only operated well onVFO， but its performance was improved. The turbine inlet temperature was lower at a given output with VFO than with either natural gas or diesel fuel. This phenomenon is due to the increase in exhaust mass flow provided by the addition of steam in the diesel for thevaporization process. Following the tests， a thorough inspection was madeof materials in the combustion module and on the gas turbine， which came into contact with the vaporized fuel or with the combustion gas. The inspection revealed no harmful effects on any of the components due to the use of VFO.
The VFO technology provides a means of converting natural gas systemsto liquid fuel without requiring new fuel liners， nozzles， and control systems.However， VFO also offers a method of treating contaminated fuel. The VFO process vaporizes only a portion of the liquid fuel; the contaminants stay in the remaining liquid fuel. The remaining liquid can be utilized either as fuel or as feedstock for other processes. It has been found that if 90% of the fuelisvaporized， the remaining 10% provides the heat required for vaporization. The heat required to vaporize the liquid fuel is recovered in the gas turbine asheat added into the combustion can， so the process is very efficient. The only loss is the energy in the heated gases leaving the vaporizer exhaust.
The overall costs for a VFO unit can be lower than the costs of con-ventional liquid fuel treatment plants. The U.S. Department of Energy conducted a survey that showed that the costs of operating a liquid fuel treatment system over a 20-year period is approximately .0.50 MMBtu output. This cost includes the initial capital investment， maintenance， and operating costs. The initial cost of a VFO unit with an output of 800 MMBtu/hr (required for a 60 MW gas turbine) is approximately.1150/MMBtu/hr output(.920，000 total). The operating costs of a VFOunit are verylow， since the only power requirement is the electrical power needed to drive several small pumps. The energy required to vaporize the oil is obtained from burning the unvaporized oil. Any additional expense in operating a VFO system results from maintenance. Maintenance will be minimal with properly selected components.
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燃气涡轮工程手册 Gas Turbine Engineering Handbook 2(72)
