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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TURBINE AUXILIARIES (OIL SYSTEM -LUBE ) PART-II ABC OF THERMAL POWER PLANT

PART-II

OIL SUPPLY DATA FOR A TYPICAL 500MW SET MANUFACTURED BY 

BHEL

MAIN OIL TANK, RATED CAPACITY:                       25/40             Cu . M

Ist OIL FILLING (ESTIMATED):                                   47.5                Cu . M

FLUSHING OIL QUANTITY (ESTIMATED):               28.5              Cu . M

OIL TEMP. AT COOLER OUTLET,                               38 TO 45 DEG C.

TEMP. RISE OF OIL IN BEARINGS                              20 TO 25 DEG C

OIL PUMPS

M.O. PUMP     A.O. PUMP       E.O. PUMP                         J.O.PUMP

      1                      2                          1                                  AC : 2             DC : 1

                                        

                                             CAPACITY (RATED)

      

    75                     89.25                     30                                    1.53              dm3/s

                                               

                                   DISCHARGE PRESSURE (GAUGE)

       

    8.6                     6.2                        2.3                                   178                 BAR

                                                           

                                                       SPEED

    50                   24.75                       24.3                                49.42                         /s

A Few erection points need to be remembered during erection of Lube line of turbine

1. Lube system includes jacking oil line. Jacking oil is used to lift rotor from bearing 

during starting .

2. As these lines requires lot of small items including fastners , o-ring , gasket, small 

bore pipes , prefabricated pipes, valves ,supports  etc a systematic material 

management is required to reduce the time cycle. No pipes to be kept open at the end. 

All pipes to be cleaned by compressed air before erection.

3. To start the work oil canal and oil room front availability is must.

4. All the pipelines joints small bore / large diameter should be tig welded in root.

5. Temporary pipes required for oil flushing to be made during erection itself so that 

last minute fabrication is not necessary.

6. Match up, weld and examine the prefabricated connecting pieces of the discharge 

and suction nozzles prior to the final erection of the first bearing pedestal.

7. Other matching and welding work to be done when the bearing pedestal is full 

assembled.

8. The direction of flow of the oil temperature control valve should be ensured as 

indicated by markings on the valve itself.

Jacking Oil Lines

9. Once the line has been welded to the bearing pedestal, fit a protection plate to 

protect the line in this area.

10. Ensure that oil vapor extraction lines are laid with a gradient descending constancy 

towards the main oil tank without low points. A drain loop at the lower end of this line 

upstream from the blowers return drains to the oil tank.

11. To avoid fire hazards, do not route oil lines near lines or components at high 

temperature.

Oil tank with pump motor on the top.

Typcal 500MW lub oil scheme is given above ( BHEL make sets) 

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TURBINE AUXILIARIES (OIL SYSTEM -LUBE ) PART-I ABC OF THERMAL POWER PLANT

In continution of my last dispatch regarding Generator Gas system two

photographs of the system is attached.

TURBINE  LUBRICATION OIL SYSTEM 

 Turbine lubrication system is the most important auxiliary system in TG Package. As 

I discussed seal oil system of Generator , lubrication system of Boiler auxiliaries like 

FANS ( ID ,FD and PA) ,Mills and Airheaters. Therefore it is felt prudent to discuss 

the oil system of Turbine .

The Turbine Lube Oil System functions to provide storage, cooling, and continuous 

purification of the lubricating oil required for the main turbine and generator.

Turbine lube oil system contains following equipments and piping.

- A Turbine oil tank

- 2 Nos AC motor driven pumps for lubrication system

- One main oil pump ( coupled with main turbine )

- One Jacking oil pump ( 100%)

- One DC lube oil pump ( 100%)

- Two oil coolers ( 2x100%) with cooling water connection and change over valves.

- Duplex  oil filter

- Instrumentation Racks and Instruments local and remote.

- Turbine oil purifier portable having capability purification of 20% of tank volume.

- A central oil purification system.

- Piping portion of them pre- fabricated and rest are site routed.

-Two full capacity oil vapour extractor.

Piping shall be routed in a manner to avoid crossing or being directly above any 

steam lines and to allow gravity drainage where possible. The high-pressure supply 

piping shall be guarded by low-pressure return piping. Coolers and pumps shall be 

physically located in the oil reservoir. The supply and return piping shall be sloped to 

avoid air pockets and to allow proper drainage. Total erection jobs takes around 04 to

05 months depends up on the readiness of the Oil canal , Positioning of Pedestals (brg)

oil room including oil cooler foundations ,tank foundations other small foundation 

etc. Clean pipes and enviornment will help to reduce the oil flushing time . Therefore 

a system of preservation ,cleaning by compressed air is must during erection. All 

welding on pipelines to be completed otherwise it will be difficult to do it afterwards

due to potential fire hazards.

Oil tank with instruments are shown in the picture. Pumps are installed on the tank.

continued
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GENERATOR AUXILIARIES (GAS SYSTEM ) PART-III ABC OF THERMAL POWER PLANT

GAS SYSTEM: Generator is cooled by introducing H2 gas as coolant. Heated H2 gas is cooled on Hydrogen cooler attached with generator. Primary water cooler and Hydrogen Cooler is cooled by DM water supply from the system either from CEP discharge or closed loop ACW system.

Use of H2 gas needs special attention because if it mix with air it may explode. Therefore safety precaution is paramount in case of Gas system. No half measure to be taken during erection and commissioning of the system. Only experienced personal should handle the system with safety precaution. I will outline the gas system required for the generator in brief.

The gas system consists of the following components:

- CO2 cylinders

- H2 cylinders

- N2 cylinders

- Gas dryer

-Gas valve manifold

Hydrogen Gas with Purity of 99.7 % minimum is charged from the cylinders to the manifold . The cylinder pressure is much higher than the required pressure . Therefore two parallel connected pressure reducing valves are used to take care of expansion.

As a precaution against explosive mixtures, air must never be directly replaced with hydrogen during generator filling not the hydrogen replaced directly with air during the emptying procedure. In both cases, the generator must be scavenged or purged with an inert gas, carbon dioxide (CO2) being used for this purpose.

CO2 is also supplied in liquid from and in compressed condition. During CO2 filling  temp control is necessary and is provided in the rack to save from excessive cooling.

To remove the CO2 from the generator,(during commissioning or on shut down) a compressed air supply with compressed air filter is connected to the general air system of the power plant. Under all operating conditions, except for CO2 purging, the compressed air hose between the filter and the generator pipe system should be physically disconnected. This is to avoid any contact with Hydrogen and air.

A gas valve rack is furnished with a mini diagram on the face of the panel to show the system . The valves used in the gas system have rubber/metal sealed valve seats to ensure gas tightness.

For measurement of Pressure transmitters are used. Also analyser , purity meter is also used in the instrument panel.

A small amount of the hydrogen circulating in the generator for cooling is passed through a gas drier. The gas inlet and gas outlet pipes of the gas dryer are connected at points of the generator with different static heads(differential fan pressure), so that the gas is forced through the dryer by the differential pressure only. Gas drier is electrically operated with temperature control.

A typical PID diagram is attached (BHEL make) below.

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GENERATOR AUXILIARIES (PRIMARY WATER SYSTEM ) PART-II ABC OF THERMAL POWER PLANT

We are breifly discussing the important auxiliary system of Generator . In part-i

we discussed about the seal oil system of generator. Now i will describe briefly

about primary water system used in power house of 500 MW above rating sets.

The treated water used for cooling the stator winding, phase connectors and 

bushings is referred to as primary water in order to distinguish it from the 

secondary coolant (raw water, or condensate). The primary water is circulated in 

a closed system and dissipates the absorbed heat to the secondary cooling water

The pump is supplied with hot primary water from the primary water tank, and delivers the water to the generator via the coolers. 

Primary water system comes as a skid only pipelines and cabling connections are to be made after erection. Skid erection gives front for piping erection and this job can be done  independently . However the total piping job including impulse

piping of instruments to be done by SS material. Stator purity is challenge to erection and commissioning engineer therefore system should be leakproof . O2

measured in the stator water in p.p.b. ( parts per billion).

The skid contains 2x100% pumps , 2x100% coolers , filters , primary water tanks ,necessary valves and insrtumentations. A typical PID is given below.

Flow path I of primary water is used for cooling the stator winding.

This flow path routes the water to the manifold at the exciter end and from there to the stator bars via insulating hoses. Each stator bar is connected to the manifold by a separate hose. The cooling water flows through hollow conductors towards the turbine end of the generator. After exiting the stator bars, the water flows through insulating hoses to a water manifold from where it is rerouted to the primary water tank.

The other flow path is for cooling the phase connector and bushings.

The bushings and phase connectors are made of thick-walled copper tubes carrying the cooling water. The 6 bushings and the phase connectors, which are arranged in circular fashion around the stator-end winding, are interconnected in such a manner that 3 parallel flow paths are established. The cooling water is admitted from outside the generator through 3 bushings and exits through the other 3 bushings.

The secondary water flow through the primary water cooler is automatically controlled to ensure that the generator temperature is maintained at a constant level under different load conditions. 

continued to part-iii

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GENERATOR AUXILIARIES (SEAL OIL SYSTEM ) PART-I ABC OF THERMAL POWER PLANT

Till  last dispatch I have outlined the installation of turbine and generator of thermal power plant briefly with the help of photos. I have also discussed what are pitfalls during erection . From now onwards I will discuss about few important systems /processes required for Turbine and Generator so that readers can have an idea of the total system of a power plant. I will first discuss about the Generator System.

 Shaft seals supplied with pressurized seal oil are provided to prevent hydrogen losses at the shaft and  the ingress of air into the hydrogen-cooled generator. All generators having rating more than 500 MW stator winding is cooled by water and rotor winding is cooled by Hydrogen. Stator water and Hydrogen is again cooled by water as secondary cooling through stator water cooler and hydrogen cooler. As long as the seal oil pressure in the annular gap is more than the gas pressure in the generator, no hydrogen will escape from the generator housing. During normal operation, the air side seal oil pump (AC) draws the seal oil from the seal oil storage tank and feeds it to the shaft seals via coolers and filters. The seal oil supplied to the shaft seals which drains towards the air side through the annular gaps between the shaft and seal rings is returned to the seal oil storage tank. For the air side seal oil circuit, three seal oil pumps are provided with one of the three pumps always in operation. In the event of a failure of the pump in service due to a mechanical or electrical failure, the second pump automatically takes over. If both pumps fail, the seal oil supply is taken over by the stand-by pump without any interruption.

During normal operation, the hydrogen side pump draws the seal oil from the seal oil storage tank 

and feeds it to the shaft seal via coolers and filters. The seal oil supplied to the shaft seals which 

drains towards the hydrogen side through the annular gaps between the shaft and the seal rings is first collected in the generator pre-chambers and then returned to the seal oil tank.

Oil pressures which exceed the generator gas pressure are required to ensure proper sealing of the generator. With the seal oil pumps in operation, the seal oil pressure is controlled by differential pressure valves. The first valve controls the seal oil pressure after two equal-priority ac air side seal oil pumps. The pressure after the stand-by seal oil pump is separately controlled by the second valve. Depending on the valve setting and the impulse oil pressure prevailing (seal oil pressure and hydrogen casing pressure), a larger or smaller amount of oil is returned to the suction pipe so that the required seal oil pressures is established at the shaft seals . A typical seal oil circuit is given below. Now seal oil system is coming as a skid item where every item is connected ,pre-wired and instrumentation completed. Only job is left to connect the lines from different places with proper slope. However only small disadvantage is there i.e. the size of the skid is fairly big because of cooler and tank fitted on it. If proper co-ordination is not done there will be problem on shifting the same to foundation in one piece. One must keep in mind pre-plan its path before hand.

typical seal oil system P&ID diagram of BHEL supplied 5000MW set.
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