TCONDENSER - AUXILIARIES OF STG SETS -ABC OF THERMAL POWER PLAN

Till last dispatch I have given an outline of  Turbine ,Generator erection including some   detail of integral piping specially  Lube oil ,control oil , drain lines ,seal steam  lines etc. From today onwards   I will describe the major auxiliaries likes Condenser , pumps and their drive turbines , heaters and other items . I receive number of mails from supervisors and young engineers for auxiliaries erection details therefore  I will try to answer all their queries in my subsequent dispatches. 

In my working time I have come across two distinct type of set one is Russian and other is German. For a given capacity like 200 MW set Russian condenser work is very less compare to German condenser. Russian condensers are pre- fabricated  up to tube supporting plate and box has to inserted and assembled . However for German design set like KWU /Siemens every item needs to be assembled i.e. starting from base assembly to the making of the box therefore time  taken for condenser erection is more than Russian set. I have never worked in Chinese sets therefore feedback is not available with me. I request readers to enlighten me in this regard. One more recent development in 660MW Siemens deign the base plate is tilled half a degree and instead of spring support bearings are provided below the base plate. There may be some other changes but not that significant during erection.

I will outline my discussion based on BHEL make 500MW. However I will use photographs of 660 MW set so readers should not get confused about the size.

   
  The condenser is a box type construction with divided water box design double flow; two pass 

which facilitates the operation of one half of the condenser while other half is under maintenance. 

The steam space is of rectangular cross-section with integral air-cooling  section from where air and non–condensable gases are drawn out with the help of air evacuation equipment.

The surface condenser is mounted on spring supports. The condenser is welded with   the exhaust hood of the low-pressure turbine. The tube plates are welded with the water chambers. Condensers are provided with domed shape water box. The condenser tubes are supported within the condenser shell by tube support plates. The condenser is installed in such a way that all condenser tubes are drained automatically into the condenser water Condition has been provided with an extension suitably to connect it to the turbine exhaust opening. Adequate internal clearance is provided. The rigid construction results in a sound-condenser combination for trouble free operation.  

The water boxes of the condenser have been designed for smooth entry and uniform distribution of cooling water to all the tubes. The water boxes are removable type and have been provided with necessary hinged manholes for easy access to the interior for inspection. Each water box has been provided with a vent and drain connection. The circulating water connections of adequate size have been provided with water boxes. The condensate produced in the condenser & drains entering through flash vessels collect in the hot well from where the pass to the condensate pumps.

CONTINUED PART -II

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TURBINE AUXILIARIES (CONTROL OIL SEAL STEAM ,DRAIN SYSTEM ) PIPING ABC OF THERMAL POWER PLANT

OTHER IMPORTANT MISC. INTEGRAL PIPING SYSTEM IN TURBINE ISLAND

A. Control Oil system.

In 500 MW Units, fire Resistant Fluid (FRF) used for the control systems and LP Bypass system mainly to 

avoid fire accident in case of leakage of working fluid over high temperature parts of turbine.

This system consists of following equipment.

a. A FRF tank with pumps mounted .

b. Oil vapour exhausters. 

c.  Filters  and FRF coolers.

The process pertains to FRF system is similar to TG lube oil system. 

However Piping size of control oil system is small bore piping with some 

exception.

The fluid circulated in the system is divided for different purposes. Such as control fluid,

secondary fluid, Trip fluid and start up fluid etc. Control oil transmits signal from

Governing Rack ,LP Bypass rack , Spray water racks etc to equipments like Control

valves ,IPCV , Extraction valaves , LP Bypass valves etc.

Precaution needed during erection stage for small bore piping.

A. Control oil piping is small bore piping that includes pipes , gasket , different size “ O –

ring” , fastners and other assorted fittings  for sealing purpose. Therefore it is requested to

make a check list of each line and supervisor should monitor the completion by using proper

material at proper place. This will reduce time during HT of the line and also save time and

money during flushing. Please remember FRF is very costly fluid.

B. Piping erected as ascending radient should have minimum 67 mm(1:15) slope.

C. Descending gradient should have minimum 175 mm slope.

E. Maintain gradient as far as possible if high point is unavoidable then provide venting

provision with orifice.

SEAL STEAM SYSTEM

Seal steam system comprises of following sub systems :

  

Seal Steam Lines, valve Stem Steam Leak-Off Lines and Seal Ring Steam Leak-Off Lines.

In laying these lines, provide sufficient compensation for thermal expansion. The service

temperature for all lines can be assumed to be approximately 450 degC. These pipes expand

by approximately 6 mm/m between the cold state (initial temperature 20 degC) and the hot

state.

Seal pipelines to be connected to the cylinder only after full assembly.

Seal and leak off steam pressure is very very low therefore impulse line for pressure

measurement should carefully laid to avoid pulsation of signal.

DRAIN SYSTEM

One of the important integral piping system contains small bore to large bore piping

including numerous motorised valves , manual valves and pipe fittings. Insulation of the

line is also an important criteria for  drain piping.

 All drain lines shall have as steep a gradient as possible, an all cases at least 20

mm/m.

 In erecting these lines, provide sufficient compensation for thermal expansion. The

service temperature in plant can be assumed to be approximately 450 deg C.

 These pipes expand by approximately 6mm/m between the cold state (initial

temperature 20 OC) and the hot state.

 On drain lines made from thick-wall piping, ensure straight pipe sections at least 500 mm

long between the drain sockets (on casings and pipes) and the first bend in the pipe.

A few PID diagrams of different system ( of BHEL make set) are attached .

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