161

What are the objectives of turbine bearing lubrication?

The objectives of bearing lubrication are as follows:

v To provide a hydrodynamic oil wedge between the bearing and the shaft, to reduce friction.

v To provide an oil flow to maintain the white metal (Babbitt metal) of the bearing below 110°C.

162

What are the sources of heat inside a turbine bearing?

The sources of heat inside the bearing are:

a. Thermal conduction

b. Friction between the oil film, the journal (portion of the shaft inside the bearing), and the white metal of the bearing

c. Turbulence within the oil itself

163

What are Disaster Management Plans (DMPs)?

Planning the response strategies, for meeting the emergencies caused by major accidents/ disasters, prior to their occurrence, are termed as Disaster Management Plans (DMPs).

Disaster Management Plans (DMPs) if put to practice, can reduce vulnerability to hazards and allow the plant workers to cope up with disasters effectively.

DMPs cannot be considered in isolation or act as a substitute for maintaining good safety standards in a plant. The best way to protect against major accidents occurrence is by maintaining very high levels of safety standards.

DMPs does not avert or eliminate the threats, instead it focuses on creating plans to decrease the impact of disasters. Failure to create a plan could lead to damage to assets, human mortality, and lost revenue.

164

What are the five phases generally involved in case of an emergency?

Generally, the following five phases are involved in an emergency:

v  Discovery and Notification: An event with an imminent threat of turning into an accident must first be discovered and the discoverer quickly notifies the same to the plant safety officer.

 

v  Evaluation and Accident Control Initiation: Based on the evaluation of available information, the safety officer makes a rapid assessment of the severity of the likely accident and initiates the best course of action.

 

v  Containment and Counter Measures: Action is first taken to contain and control the accident by eliminating the causes which may lead to the spread of accident. Measures are also taken to minimize the damage to personnel, property and environment.

 

v  Cleanup and Disposal: After the accident is effectively contained and controlled, the cleanup of the site of the accident and safe disposal of waste generated due to the accident are undertaken.

 

v  Documentation: All aspects of accidents, including the way it started and progressed as well as the steps taken to contain and the extent of the damage and injury, are documented for subsequent analysis of accident for prevention in future, damage estimation, insurance recovery and compensation payment.

165

What determines the level of emergency/ disaster?

Severity of accident and its likely impact area will determine the level of emergency and the disaster management plan required for appropriate handling of an emergency.

166

What are the different levels of fire emergency and explain in brief the action needed for each level of emergency?

Emergency levels and the action needed for each level are explained below:

Level 1 Emergency

A local accident with a likely impact only to immediate surroundings of accident site, such as, local fires and limited release of inflammable material.

The impact distance may not be more than 15 m from the site of primary accident and may require evacuation of the building/area where accident occurred and utmost the adjacent building/area.

Level 2 Emergency

A major accident with potential threats to life and property up to 500 m distance requiring the evacuation of all personnel from the threatened area except the emergency response personnel. Larger fires, release of large quantities of inflammable materials belongs to emergency level 2.

Level 3 Emergency

An accident involving a very serious hazard and with likely impact area extending beyond 500 m from the operational area, such as, major fire, very large release of inflammable material. Major fires will usually have the triggering effect resulting in the propagation of explosion. In a level 3 emergency, evacuation of population in villages, if any, adjoining the operational area may sometime become necessary if threatened area extend to populated village area adjoining the site of the primary accident in a direction of maximum impact.

167

What are the special design features considered for piping used in jacking oil and lubricating oil systems against oil leakage and fire hazards?

Special design precautions against oil leakage and fire hazards are taken for piping used in jacking oil and lubricating oil systems.

The oil piping is sized to have a velocity only between 1 and 5 m/s.

An enclosure or a duct is installed around the oil piping at the pump discharge.

The number of pipe joints is minimized by maximizing the length of pipe runs.

All pipe joints are welded class 1 type.

At the exit from the ducted area, a protective pipe is installed around the pressure oil pipe. This is done to contain and detect any oil leakage.

The piping between the pump and the filters is made of mild steel, and stainless-steel piping after the filters to minimize corrosion.

If the air is not vented through the bearings, an automatic air venting of the piping from its highest points to the oil tank is installed.

Air vents to the oil tank are installed on the oil filters. They vent any air that accumulates during operation or maintenance to the oil tank.

168

What is the function of lube oil coolers in the turbine lube oil system, and explain in brief the design features of lube oil coolers?

The function of lube oil coolers (heat exchangers) is to lower the temperature of the oil leaving the turbine bearings, below the acceptable limit.

Redundant coolers are provided to allow maintenance to be performed while the unit is operating.

The normal arrangements are 3 X 50% or 2 X 100% coolers.

The oil coolers are installed vertically.

The water flows through the tube in a two-pass arrangement.

The oil flows on the shell side of the coolers through a series of baffles.

The shells of the coolers are generally made of mild steel and the tubes of titanium.

The tube bundle has a floating tube plate to accommodate thermal expansion.

The heat dissipated by each cooler is around 2 MW.

The oil filters are integral with the cooler shell on some units. An automatic bypass of the oil coolers is normally installed. It allows the oil to bypass the cooler upon an excessive pressure drop across the cooler.

The automatic control system is based on the oil outlet temperature.

169

The steam leaking from the turbine glands represents the main source of contamination for the lubricating oil.

The steam condenses when it comes in contact with the bearing housing. The condensate becomes dispersed through the oil.

The used oil normally contains wear particles, oxides, soluble acids, and sludge. These impurities must be removed from the oil to extend its life and maintain adequate lubrication.

The on-line systems used to these remove impurities include centrifugal separation systems and static oil purifiers.

170

What are the functions of lube oil used in a steam turbine?

The oils used for steam turbines must provide the following functions:

v  Removal of heat generated in the bearing housing

v  Removal of impurities from the bearings

v  Minimization of corrosion and oxidation

The lube oil contains additives for the prevention of oxidation, corrosion, and foaming.