Answer EKM Question 5
Q5. Explain why the following problems occur in turbocharger nozzles, shrouds and blades, their effects on turbocharger operation and remedies: – A. Build-up of deposits; B. Hot corrosion; C. Erosion.
Answer: A. Build-up of deposits:
(a) When combustion is clean, the deposits found within the nozzles and hlading of the exhaust turbine are usually sodium compounds in the form of sulphates vanadium compounds and vanadiu compounds in the form of oxides.
(b) Some additives used in the cylinder lubrication may be found as ash.
(c) If combustion is dirty, sooty deposits and carbonaceous materials may be found. These deposits may be due to, impurities in the fuel or due to poor combustion.
(d) Poor combustion is caused by operating engine at low loads for prolonged periods.
(e) When nozzle and rotor blades become dirty the symptoms are
(i). Rising exhaust gas temperature at turbine inlet.
(ii). Falling speed (RPM) of the turbine.
(f) The exhaust gas temperatures rises because the gas gives up more kinetic energy before it enters nozzle & Blades.
(g) This kinetic energy is converted into heat and consecniently increases the temperature.
(h) Dirt in nozzle and blades change the velocity pattern Of the gases passing through them, this prevents turbine working efficiently and the speed of rotation falls.
(i) When turbine operates at lower speeds, charge air delivery is reduced and this causes cylinder exhaust gas temperature to rise.
(j) In order to minimize build-up of deposits engine is recommended to be operated at high loads and frequent dry washing is essential.
(k) If fuel contains large percentage of MCR (Micro Carbon residues) and CCR (Conardson carbon residues) more than 20%, this will lead to carbon depoSitiwhich will cause pitting on valve seats.
B. Hot corrosion:
(a) Hot corrosion is caused due to Vanadium & Sodium in the fuel in a 3:1 ratio which will result in the production of sodium vanadate and further oxidises in to a compound Vanadium pentoxide which has a low melting point.
(b) These are highly corrosive in nature and will lead to bearing corrosion.
(c) Proper purification most be done to prevent ingress of sodium through sea water contamination.
Vanadium & Sodium
Va = 300-600mg/Kg
If the fuel is contaminated with sea water, there will be deposition of Vanadium Pentaoxide $\displaystyle \small \mathrm{(V_2O_5)}$ .
At 675°C $\displaystyle \small \mathrm{V_2 + O_2\rightarrow V_2O_5}$ — Vanadium Penta-Oxide.
The vanadium cannot be removed by purification. As the percentage of Na increases, the melting point of $\displaystyle \small \mathrm{(V_2O_5)}$ will reduce and when the ratio is 1%, 3:1, the melting point reduces, this vanadium pentoxide gets deposited on the metal surfaces on the exhaust valve, Turbine blades, Shrouds. It will be in the form of hard corrosive scales that will cause the high temperature corrosion.
C. Erosion
- Ash and catalytic fins are the main reasons for erosion. Silica, Alumina are highly abrasive which causes erosion in turbine blades, nozzle ring etc.
- These carried over in the fuel system due to improper purification and filtration.
- Erosion may also be caused due to presence of iron ore dust through air suction. (Bulk carriers)
Remedies;
1. Proper filtration
2. Purification
3. Draining.
How in each, the problem may be minimized.
(a) Heavy fuel oils with high metal concentrations like sodium, Vanadium, Nickel and lead can cause accelerated fouling and tenacious deposits and corrosion.
(b) To compensate for the effects of these metals, on T/C blading, a chemical inhibitor can be mixed with the heavy oil to modify the chemical and physical properties of the resulting ash.
(c) These chemical inhibitors are added to the heavy fuel oll In proportion to the metal content of the fuel.
(d) Fuel additives containing magnesium and silicon active metallic ingredients have demonstrated results.
(e) The chemical additive can be injected into heavy fuel oil by a metering pump.
(f) A pump or a static mixer will improve the mixing of fuel additive into the fuel oil flow.
Other effective ways of reducing corrosion, erosion & deposits.
(a) Use of fuel with low content of vanadium & uncritical vanadium sodium ratio.
(b) Decrease of sodium Content in heavy fuel oil to the lowest level by purification. prevent exhaust gas temperatures higher than 500°C
(c) Installation of filters in charge air system.
(d) Addition of magnesium salt base heavy fuel oil additive have shown favorable results in pushing reaction of temperature upwards.
(e) Fuel to be tested prior putting it into use and purification to be monitored.
(f) Drain settling & Service tanks regularly.
(g) Avoid prolonged low load operation.
Answer: A. Build-up of deposits:
(a) When combustion is clean, the deposits found within the nozzles and hlading of the exhaust turbine are usually sodium compounds in the form of sulphates vanadium compounds and vanadiu compounds in the form of oxides.
(b) Some additives used in the cylinder lubrication may be found as ash.
(c) If combustion is dirty, sooty deposits and carbonaceous materials may be found. These deposits may be due to, impurities in the fuel or due to poor combustion.
(d) Poor combustion is caused by operating engine at low loads for prolonged periods.
(e) When nozzle and rotor blades become dirty the symptoms are
(i). Rising exhaust gas temperature at turbine inlet.
(ii). Falling speed (RPM) of the turbine.
(f) The exhaust gas temperatures rises because the gas gives up more kinetic energy before it enters nozzle & Blades.
(g) This kinetic energy is converted into heat and consecniently increases the temperature.
(h) Dirt in nozzle and blades change the velocity pattern Of the gases passing through them, this prevents turbine working efficiently and the speed of rotation falls.
(i) When turbine operates at lower speeds, charge air delivery is reduced and this causes cylinder exhaust gas temperature to rise.
(j) In order to minimize build-up of deposits engine is recommended to be operated at high loads and frequent dry washing is essential.
(k) If fuel contains large percentage of MCR (Micro Carbon residues) and CCR (Conardson carbon residues) more than 20%, this will lead to carbon depoSitiwhich will cause pitting on valve seats.
B. Hot corrosion:
(a) Hot corrosion is caused due to Vanadium & Sodium in the fuel in a 3:1 ratio which will result in the production of sodium vanadate and further oxidises in to a compound Vanadium pentoxide which has a low melting point.
(b) These are highly corrosive in nature and will lead to bearing corrosion.
(c) Proper purification most be done to prevent ingress of sodium through sea water contamination.
Vanadium & Sodium
Va = 300-600mg/Kg
If the fuel is contaminated with sea water, there will be deposition of Vanadium Pentaoxide $\displaystyle \small \mathrm{(V_2O_5)}$ .
At 675°C $\displaystyle \small \mathrm{V_2 + O_2\rightarrow V_2O_5}$ — Vanadium Penta-Oxide.
The vanadium cannot be removed by purification. As the percentage of Na increases, the melting point of $\displaystyle \small \mathrm{(V_2O_5)}$ will reduce and when the ratio is 1%, 3:1, the melting point reduces, this vanadium pentoxide gets deposited on the metal surfaces on the exhaust valve, Turbine blades, Shrouds. It will be in the form of hard corrosive scales that will cause the high temperature corrosion.
C. Erosion
- Ash and catalytic fins are the main reasons for erosion. Silica, Alumina are highly abrasive which causes erosion in turbine blades, nozzle ring etc.
- These carried over in the fuel system due to improper purification and filtration.
- Erosion may also be caused due to presence of iron ore dust through air suction. (Bulk carriers)
Remedies;
1. Proper filtration
2. Purification
3. Draining.
How in each, the problem may be minimized.
(a) Heavy fuel oils with high metal concentrations like sodium, Vanadium, Nickel and lead can cause accelerated fouling and tenacious deposits and corrosion.
(b) To compensate for the effects of these metals, on T/C blading, a chemical inhibitor can be mixed with the heavy oil to modify the chemical and physical properties of the resulting ash.
(c) These chemical inhibitors are added to the heavy fuel oll In proportion to the metal content of the fuel.
(d) Fuel additives containing magnesium and silicon active metallic ingredients have demonstrated results.
(e) The chemical additive can be injected into heavy fuel oil by a metering pump.
(f) A pump or a static mixer will improve the mixing of fuel additive into the fuel oil flow.
Other effective ways of reducing corrosion, erosion & deposits.
(a) Use of fuel with low content of vanadium & uncritical vanadium sodium ratio.
(b) Decrease of sodium Content in heavy fuel oil to the lowest level by purification. prevent exhaust gas temperatures higher than 500°C
(c) Installation of filters in charge air system.
(d) Addition of magnesium salt base heavy fuel oil additive have shown favorable results in pushing reaction of temperature upwards.
(e) Fuel to be tested prior putting it into use and purification to be monitored.
(f) Drain settling & Service tanks regularly.
(g) Avoid prolonged low load operation.
Comments
Post a Comment