Turbine Flashcards
what prevents the steam from leaking at a point where rotating shaft penetrates through the casing?
since the shaft penetrates through the casing, seal is necessary to minimize the leak of steam. in small, low temperature turbine is used carbon packing ring seal. it is located directly on shaft and held in place by spring assembly. in larger turbine, labyrinth seal is used to control the leakage. in many turbine designs, a combination of these 2 seals are used at the end of shaft.
function of hydrogen gas
used to cool the winding in electric generators. it is the most effective operation result on generator compare to other method bcs it provides high thermal conductivity. hydrogen losses can also occur through the generator’s rotor seal and is required makeup hydrogen. most plant have storage tanks that are replenished by truck deliveries. and larger facilities have onsite production hydrogento increase convenience.
the purpose of thrust bearing and how it is cooled
✧ bcs of the axial thrust along the shaft that results from the difference in steam pressure across the stages of turbine, thrust bearings are used to maintain the clearance between moving blades and stationary portion in each stage of turbine.
✧ it is cooled by water jacketing; in others, oil is circulated through a cooler
what are the components of generator?
✧ frame
✧ stator core and winding
✧ rotor and winding
✧ bearing
✧ cooling system
2 general types of condensers
✧ direct contact type condenser
- cooling water is sprayed directly to the exhaust steam from the turbine, where mixtures of water with steam condenses the steam
✧ surface condenser
- the cooling water and the exhaust steam remain separate
describe the direct acting
it operates like a radiator in an automobile. exhaust steam flows from the turbine outles through the external finned tubes. air is blown on the tubes and the steam is condensed. the condensate flows to the condensate storage tank, from which is pumped through the feedwater heater chain and returned to the boiler. this is the most used design
describe the indirect acting
the turbine exhaust steam is condensed by water cooling loop in a convenctional surface condenser. the cooling water then rejects heat to the atmosphere in a dry cooling tower by air flowing across the external finned tubes
describe the cooling tower
a special direct contact heat exchanger, where warm cooling water from the condenser is brought into the direct contact with relatively dry air. the heat transfer rate depends on maximizing the contact area between water and air and the length of time for this contact
common features of cooling tower
✧ an air circulation system
✧ a water distribute or spray system
✧ packing/fill to maximize the contact between water and air
✧ a cooling water collection and discharge basin
✧ mist eliminator to minimize droplets carry-over and water losses
the problems associated with these gases can be minimized by good operating practices that prevent their entry into the condensate and boiler system
these procedures should include:
✧ properly operated condensate pump tank vents and good deaeration, which can keep oxygen and carbon dioxide out of the system
✧ demineralization, which can reduce the amount of alkalinity in boiler feedwater and thus, the amount of carbon dioxide that has been developed by alkalinity breakdown
✧ the use of condensate polishing, which is effective for the removal of hardness and corrosion product caused by leakage into the system
✧ the use of chemical treatment to control carbon dioxide and oxygen which supplements the mechanical process
in large industrial power plant, the four-stage turbine extraction steam offer to a type of feedwater, what is the name of this feedwater?
this feedwater heaters are also called Deaerator. It serves a dual purpose of heating the feedwater to improve plant efficiency and deaerating the feedwater to remove gases that can cause corrosion to equipment and piping system. it also provides storage of high quality feedwater for the boiler feed pump.
damage of feedwater heaters
✧ erosion from steam impingement
✧ tube vibration
✧ erosion and corrosion on the inlet of tube end
✧ oxygen pitting
✧ stress corrosion cracking
