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Gas Turbine Fuel Oil to Gas Problems and Measures
1. Fuel nozzle and flame tube inspection and cleaning For the dual fuel nozzle, before reforming natural gas, it should be disassembled and overhauled to clean up impurities and residual oil in the fuel passage, otherwise it will have the following hazards: (1) remain in the nozzle Oil under high temperature carbonization coke, block the fuel flow path, the unit can not switch to the oil fuel operation, oil fuel system lost reserve function. (2) Carbonized coke and ash particles are likely to cause clogging of the cyclone, causing the deformation of the airflow field at the head of the flame tube, which may cause elongation or deflection of the flame, resulting in local ablation or burn-through of the flame tube. (3) After the cyclone is clogged, the combustion intensity and the main airflow velocity field change between the flame tubes cause the air flow distribution between the flame tubes to be uneven, and then the pressure between the combustion chambers is unbalanced, so that the flame edge Associated flame tube from the combustion chamber pressure to the combustion chamber with low pressure, resulting in the desire to scoop pipe creep, burn through or even through the Gunnison scoop tube coat. Flame tube on the scale, coking, etc. should be completely removed. These deposits clog the cooling holes of the flame tube, resulting in the local overheating of the flame tube. At the same time, due to the uneven distribution of sediments, so that the flame tube heating is not uniform, resulting in greater thermal stress, easy to cause warpage and so on. 2. To ensure good performance of the fuel supply equipment The fuel check valve on the fuel supply manifold and the fuel check valve on the fuel supply manifold of the combustion chamber should be shut off without leakage. If the sealing performance fails, the fuel will gradually enter the combustion chamber. Leakage is very small, easy to cause fuel nozzle carbonization coke; leakage is large, the accumulation of fuel in the bottom of the combustion chamber, the unit ignition, the fuel will spontaneous combustion, resulting in local overheating deformation of the flame tube and other parts or burn through. Even if the natural gas burning, before the start of the unit, but also to test what, when the failure of the oil discharge valve to start the discharge of oil. 3.Temperature Control Line Setting Change Due to the heavy flame radiation intensity of heavy fuel oil, it is easy to cause localized high temperature deformation of the flame tube and turbine components. Meanwhile, in order to reduce the high temperature corrosion of the alkali metal compound and the vanadium compound on the hot aisles and the blades, Generally when burning heavy fuel temperature control line set value lower than the design value. After converting the natural gas into the unit, if the unit wants to improve the efficiency of the gas turbine and the efficiency of the combined cycle, the set point of the temperature control line must be increased to be close to the designed value. For example, when a factory burns crude oil, the temperature control line of the gas turbine is set to be 515 ° C and the initial gas temperature is 1073 ° C; when the natural gas is burned, the temperature control line is set to 543 ° C and the gas initial temperature is 1200 ° C. If the unit does not overhaul the hot aisle components and clean up the blade fouling, the temperature control line will be adjusted directly from 515 ° C to 543 ° C. The initial gas temperature will rise from 1073 ° C to 1200 ° C. Increasing the initial gas temperature will have the following adverse effects: (1) Increased blade corrosion. As the initial temperature increases, deposits of many foulants and compounds deposited on the blades and metal parts will be molten, especially when burning heavy fuels , Alkali metal sulfur and oxides contained in the fuel to form Na2SO4 and K2SO4. When these alkali metal salts condense as droplets on the surface of the blade, the protective oxide film on the surface of the blade is destroyed and the reformation of such an oxide film is prevented, causing the infiltration of sulfur into the metal substrate, causing rapid corrosion of the sulfide and the metal, causing Depletion of Aluminum and Chromium in Blade Base Material. In high-temperature gas, the vanadate formed by the vanadium compound is bonded to the metal part and reacts with elements such as Cr, Ni and Co of the gas turbine blades to reduce it to a vanadyl compound. And these vanadium-based compounds and precipitation of oxygen and then react to generate vanadate, forming a red and red week cycle, leading to blade corrosion. (2) Caused by hot aisle local high-temperature combustion engine running for a certain period of time, due to the fuel ash, impurities and incomplete combustion will be in the static and dynamic blade fouling scaling, long-term operation will surely cause serious scaling, and even blocked the cooling holes. If under such conditions, the initial gas temperature increased from 1073 ℃ to 1200 ℃, serious scaling area, due to lack of cooling, resulting in some parts of the high temperature, if these parts for a long time in the high temperature zone, the metal resistance Fatigue strength and creep resistance decreased, changes in the metallurgical structure, resulting in local cracks, or even pieces. (3) Increasing the vibration of turbine After increasing the initial temperature, there are many foulants originally attached to the flame tube, the transitional section and the first stage vanes, which are molten and will be blown off by the high-temperature air flow to the next few stages. These molten compounds do work with the air temperature decreases, in the face of the lower temperature of the dynamic and static vanes will adhere to it. Adhered to the moving blades on the compound increased, causing the rotor unbalanced quality, causing vibration. In response to the above adverse effects, the unit should be hot aisle components (especially a nozzle) overhaul and clean up the blade fouling, so as to improve operating parameters, to improve the efficiency of the gas turbine. A factory for various reasons did not overhaul, direct conversion from crude oil to natural gas fuel operation, the measures taken are: (1) before the unit is running, the turbine leaves off-line chemical cleaning, endoscopic examination, moving, static blades No obvious loose dirt fouling, corrosion spots, detailed examination of the results recorded. (2) raise the temperature control line in stages. Increase the temperature control line to 5 ℃ ~ 10 ℃ as a stage, at each stage for a period of time to observe the load changes, the rotor vibration, chemical cleaning blade erosion, and exhaust dispersion. If the load is not reduced, the rotor vibration does not increase, there is no obvious signs of corrosion, indicating that the temperature control line operation is safe and reliable, and can further improve the temperature control line. If further increase the temperature control line, resulting in changes in load, vibration, corrosion increased, at boot time, reduce the temperature control line to ensure the safe and stable operation of the unit. According to the operating experience, it is feasible to raise the temperature control line by stages. It not only achieves the purpose of increasing the efficiency of the gas turbine and extending the service life of the gas turbine, but also accumulates operational experience and improves the ability of solving the problem.