Problems and measures of changing fuel oil to gas

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Problems and measures of changing gas turbine fuel oil to gas

for dual fuel nozzles, before changing to burning natural gas, they should be disassembled and overhauled to clean up the impurities and residual oil in the fuel channel, otherwise the following hazards will occur:

(1) the residual oil in the nozzle will be carbonized and charred at high temperature, blocking the fuel flow path, making the unit unable to switch to oil fuel operation, and the oil fuel system will lose its standby function

(2) carbonization, coking and ash particles are easy to cause blockage of the cyclone, causing deformation of the airflow field at the head of the flame tube, and the flame will stretch or deflect, causing local ablation or burn through of the flame tube

(3) after the hydrocyclone is blocked, the combustion intensity and main air flow velocity field between the flame barrels change, causing uneven distribution of air flow between the flame barrels, and then causing pressure imbalance between the combustion chambers, making the flame flow along the cross flame tube from the combustion chamber with high pressure to the combustion chamber with low pressure, resulting in creep, burn through and even burn through of the scoop tube jacket

the scale and coking on the flame tube should be completely removed. These deposits block the cooling hole of the flame tube, causing local overheating and burning of the flame tube. At the same time, due to the uneven distribution of sediment, the flame tube is heated unevenly, resulting in large thermal stress, which is easy to cause warpage and deformation

2. Ensure that the fuel supply equipment has good performance

the fuel stop valve on the fuel supply main pipe and the fuel check valve on the fuel supply manifold of the combustion chamber should be shut off without leakage. If the sealing performance of the two fails, the fuel will gradually enter the combustion chamber. If the leakage is very small, it is easy to cause carbonization and coking of fuel nozzle; When the leakage is large, the fuel accumulates at the bottom of the combustion chamber. When the unit is ignited, the fuel will spontaneously ignite, causing local overheating, deformation and even burning through of the flame barrel and other components. Even if natural gas is burned, before the unit is started, it is necessary to test whether there is oil discharged from the oil drain valve when the start fails

3. Change of setting value of temperature control line

due to the high flame radiation intensity of heavy fuel, it is easy to cause local high-temperature deformation of flame tube and turbine components. At the same time, in order to reduce the high-temperature corrosion of alkali metal compounds and vanadium compounds on heat channels and blades, the setting value of temperature control line when burning heavy fuel is generally lower than the design value. After the unit changes to burning natural gas, in order to improve the efficiency of gas turbine and combined cycle, the set value of temperature control line must be increased to close to the design value. For example, when burning crude oil in a plant, the temperature control line of the gas turbine is set to 515 ℃, and the initial temperature of the gas is 1073 ℃; When burning natural gas, set the temperature control line to 543 ℃, and the initial temperature of gas is 1200 ℃. If the unit fails to overhaul the hot channel components and clean the blade scale when changing oil to gas, directly adjust the temperature control line from 515 ℃ to 543 ℃, and the initial temperature of fuel gas will rise from 1073 ℃ to 1200 ℃. The increase of the initial temperature of the fuel gas will cause the following adverse effects:

(1) it will aggravate the corrosion of the blades

with the increase of the initial temperature, many ash deposits and compounds deposited on the blades and metal parts will be molten, especially when burning heavy fuel, alkali metals and sulfur and oxides contained in the fuel will form Na2SO4 and K2SO4. When these alkali metal salts condense into droplets on the blade surface, the protective oxidation that destroys the digital display on the blade surface can only measure some basic data. In China, energy distribution not only spreads the film with obvious regional differences in the total amount, but also prevents the re formation of this oxide film, which will make sulfur penetrate into the metal matrix, cause vulcanization and rapid corrosion of metal, and cause the dilution of aluminum and chromium in the blade matrix material

in high-temperature gas, vanadate formed by vanadium compounds is bonded to metal parts and reacts with Cr, Ni, CO and other elements of gas turbine blades to reduce to vanadium oxide based compounds. These vanadium based compounds react with the precipitated oxygen to form vanadate, forming a cycle of redox reactions, leading to blade corrosion

(2) cause local high temperature in the heat channel

after the fuel gas turbine runs for a certain time, ash, impurities and incomplete combustion in the fuel will accumulate and scale on the moving and stationary blades, and long-term operation will cause serious scaling and even block the cooling holes. Under such conditions, if the initial temperature of the gas is increased from 1073 ℃ to 1200 ℃, the area with serious scaling will not be well cooled, resulting in high temperature of some parts. If these parts are in the high temperature area for a long time, their metal fatigue strength and creep resistance will be reduced, and the metal structure will change, causing local cracks and even falling blocks

(3) the handling site of aluminum materials that cause turbine vibration does not need workers to intensify.

after increasing the initial temperature, many scales originally attached to the flame tube, transition section and first stage stationary blade are molten and will be blown away by high-temperature air flow to the next few stages. The temperature of these molten compounds decreases with the work of the air flow, and they will adhere to the moving and stationary blades with lower temperature. The compound adhering to the moving blade increases, causing the rotor mass imbalance and vibration

in view of the above adverse effects, the unit should overhaul the hot channel components (especially the primary nozzle) and clean the blade fouling when changing oil to gas, so as to improve the operating parameters and achieve the purpose of improving the efficiency of the gas turbine

due to various reasons, a factory did not carry out overhaul, and directly changed from crude oil to natural gas fuel. The measures taken are:

(1) before the operation of the unit, the turbine blades were off-line chemical cleaned. After endoscopic inspection, there were no obvious loose ash, scaling and corrosion spots on the moving and stationary blades, and the inspection results were recorded in detail

(2) improve the temperature control line in stages. Raise the temperature control line to take 5 ℃ ~ 10 ℃ as a stage, operate for a period of time in each stage, and observe the change of load, rotor vibration, blade corrosion after chemical cleaning, and the content of Milad? Nxtm8000 ultra permeable polypropylene sheet can be widely used in the field of fruit, meat products and fast food packaging. If the load is not reduced, the rotor vibration is not increased, and there are no obvious corrosion spots, it shows that the operation of this temperature control line is safe and reliable, and the temperature control line can be further improved. If the temperature control line is further increased, resulting in changes in load and vibration, and increased corrosion, reduce the temperature control line when starting up to ensure the safe and stable operation of the unit

according to the operation experience, the scheme of improving the temperature control line by stages is feasible, which not only achieves the purpose of improving the efficiency and prolonging the service life of the gas turbine, but also accumulates the operation experience and improves the ability to solve problems

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