POWER PLANT PIPINGS

INTRODUCTION

The plant and systems are designed to achieve the best possible efficiency under the specified operating conditions. The Power Cycle shall be designed with one low pressure feed water heater (de-aerator). The steam requirement of the de-aerator shall be met from the bleed of the turbine. The cooling medium is filtered water, which is circulated through a cooling tower. The water is supplied by owner at the terminal point (Raw Water Tank) from where it will pumped at the required pressure to the Cooling Tower. The cooling water temperature considered is 32 Deg C with a temperature rise of 8 Deg C across the Condenser. The Design wet bulb temperature for the cooling tower has been considered as 27 Deg C. The efficiency of the Power plant is deepens upon the water. The required quantity of raw water shall be stored in the raw water tank of capacity 1500 m3. We have

considered

river water of plant for cooling tower.

low hardness

as CaCO3

and negligible

Silica as SiO3 for the water treatment plant design. This is the basis for the selection of the multi-grade filter / RO plant and DM water treatment plant. Any change in the limits of this water analysis will impact the water treatment plant design and cost. We have not considered water softening The raw water after filtration and required dosing will be taken to the cooling tower (make up) for the condenser cooling water system. For the boiler makeup, the filtered water will be taken through the RO/DM Water treatment plant and then stored in the DM water storage tank of 20 m3. The boiler make up water stream is designed for 2 m3 / hr capacity. In case if any other water source is available for the power plant, the same may be indicated to us for design.

INPUT CONDITIONS

•

Ambient conditions and other inputs (assumed)

• Temperatures : • Design temperature for performance • Design Temperature for Electrical : 35 Deg C : 45 Deg C • Relative Humidity • Plant Design Relative Humidity • Design Wind Velocity • Seismic Coefficient : : 65.0% : As per IS: 875 : As per IS: 1893 • Soil Bearing Capacity at 2.0 m Depth • (To be reconfirmed after site location is finalized & soil investigations are conducted) • Cooling Water temperature : 20 T/m2 : 32 Deg C

FEED WATER SYSTEM

• Boiler Feed water pumps (2 Nos.) complete with coupling, base frame and drives arrangement.

• Feed regulating station for maintaining uniform level of water in steam drum.

• Stand by flow path of 100% capacity.

• Feed pump re-circulation flow under low feed pump flow conditions by automatically controlled solenoid valve installed in between feed pump and de-aerator.

• Strainers at the suction of feed water pump. • Feed line from de-aerator to feed pump suction, feed pump discharge to economizer and from economizer to steam drum.

DE-AERATOR CUM STORAGE TANK

• De-aerator with de-aerated water storage tank.

• Minimum and essential valves and fittings.

• Saddle support for placement of de-aerator on control room top.

• Level control valve with required isolation.

• Pressure control valve with required isolation.

• Feed water piping from de-aerator outlet to feed pump suction.

• Feed water piping from the outlet of level control station to de-aerator.

• Steam piping from the outlet of pressure control station to de-aerator.

DEAERATION TANK

SPECFICATION

• Type :Horizontal spray type • Design code • Design pressure :As per US standards :22.0 Kg/cm • Design material temperature • Storage tank capacity at NWLm316 • Deaeration capacitym3/hr.60

• Hydraulic test pressure :200 Deg. C.

:24 Kg/cm • Operating temperature • Operating pressure :120 Deg.C.

: 0.35 Kg/cm2 • Deaerator water inlet temp.

:45 Deg.C.

• Deaerator water outlet temp.

:120 Deg.C.

• Oxygen content in deaerator water :0.01 ppm

WATER REQUIREMENT

• The raw water shall be from the day storage hold up, under ground tank (owners scope) of 2000 m3 capacity (1500 m3 for Power Plant and 500 m3 for fire fighting) and supplied at the inlet to the raw water pumps and passed through multi grade filter (MGF) at 3.5 kg/cm2. One stream of the filtered water shall be taken to the Cooling Tower. The other stream shall be taken to RO / DM Plant as per the scheme.

• The chlorine dozing system shall be provided to prevent Algae formation and Bacteria.

• The Raw Water is pumped by the Filter Feed Pump through the Multi Grade Sand Filter (MGF) for the removal of Suspended Solids. The unit consists of quartz sand media for the purpose. The unit should be backwashed in a day or whenever the pressure drop exceeds 0.8 Kg/cm2, whichever is earlier.

WATER PROPERITES

• Hardness (ppm) • pH @ 250C • Conductivity @ 250C • Total Silica (maximum) (ppm): • Residual Hydrazine (ppm) : : : : 0 8.8 – 9.2 (after pH correction) 0.5 (microsiemen / Cm) 0.02

0.01 – 0.02

PIPING & PIPING MATERIALS

• • • • All piping system will be designed as per ASME B 31.1 and IBR. Stress Analysis shall be carried out for all critical piping as per ASME B 31.1 / IBR requirements. Supports, Spring Supports, guides, directional anchors will be selected to satisfy all the operating conditions. Drains and traps will be provided as required. • • • • • • •

The piping material selection will be based on the following recommendations

For temperature above 4240C up to 5100C - SA 335 Gr. P11 / P12 will be used For temperature up to 4240C For HP / LP chemical dosing - SA 106 Gr. B will be used - SA 312 TP 304, stainless steel will be used.

For cooling Water, Raw Water, Service Water, Safety / Relief Valve Exhaust – IS:1239 / IS:3589 ERW / EFW pipes will be used.

For service air applications, the piping will be - IS:1239.

For instrument air applications: Galvanized pipe (Iron Pipe) - IS:1239 Part I will be used.

PIPING

• Codes, Standards & Regulations

– ASME – DIN – TRD – BS – IBR

•

Codes and Standards:

• Several standards groups for have materials, written codes inspection, and design, stress analysis, fabrication, heat treatment, welding and construction of pipes and piping components. Regulations, practices, rules and laws are also available for use of piping. Certain aspects are mandatory and certain aspects are recommendatory.

The commonly American Codes and Standards on piping used

1. ASME B31.1

2. ASME B31.2

3. ASME B31.3

4. ASME B31.4

5. ASME B31.5

6. ASME B31.8

7. ASME B31.9

8. ASME B31.11

-Power Piping -Fuel Gas Piping -Process Piping -Pipeline Transportation Systems for Liquid Hydrocarbons and other Liquids.

-Refrigeration Piping -Gas Transmission and Distribution Piping Systems - Building Services Piping - Slurry Transportation Piping Systems.

Through the use of codes and standards, safety and uniform economy are obtained. The codes and standards primarily cover the following aspects: 1.

2.

3.

Factors safety Material property Thickness calculation 4.

5.

6.

Loads Load combinations Stress limits 7.

8.

Stress intensification factors Flexibility factors 9.

Supports 10. Flexibility analysis.

COMPARISON OF CODES IBR 1950 ASME SEC.I

BS 1113 DIN TRD 300 REMARKS DESIGN PRESSURE DESIGN TEMPERATUE ALLOWANCE RADIATION CONVECTION DESIGN PRESSURE WITH PRESSURE DROP 50



C DRUM DESIGN PRESSURE DRUM DESIGN PERSSURE 50



C DRUM DESIGN PRESSURE 50



C 39



C ACTUAL METAL TEMPERATURE 371



C (MIN) 35



C 35



C ECONOMISER 11



C 25



C (15 + 2 Se)



C Max. 50



C Se - ACTUAL WALL THICKNESS in mm.

WATER WALL 28



C 50



C 50



C TUBE THICKNESS FORMULA t min FACTOR OF SAFETY PD --------- + *C 2f + P Et R 1.5 , 2.7

SR SC 1.5 PD --------- + 0.005D

2f + P Et R 1.5 , 3.5

SR SC 1.5 PD -------- 2f + P Et R 1.5 , 2.7

SR 1.3 PD -------- 2f + P Et R 1.5 , 2.4

SR 1.0 P=DESIGN PR.

D=OUTSIDE DIA f=ALLOWABLE STRESS CORR. TO DESIGN METAL TEMP.

Et = YIELD STRENGTH R = TENSILE STRENGTH SR = RUPTURE STRENGTH SC = CREEP STRENGTH FOR ASME MATERIALS ALLOWABLE STRESS CAN BE TAKEN DIRECTLY FROM ASME SEC.II PART-D *C = CORROSION ALLOWANCE = 0.75mm FOR P ≤ 70 bar; 0 mm FOR P > 70 bar

TEMPERATURE LIMITS FOR VARIOUS STEEL GRADES OF TUBES / PIPES Sl.

Nominal MATERIAL SPECIFICATION Temp.

No.

Composition ASME Section-I DIN – TRD 300 BS 1113 Limit



C 01.

Carbon Steel St 35.8

St 45.8

427 02.

03.

04.

05.

06.

07.

08.

09.

½ Mo 1 Cr ½ Mo 1 ¼ Cr ½ Mo 2 ¼ Cr 1 Mo 9 Cr 1 Mo ¼ V 12 Cr 1 Mo ¼ V 18 Cr 8 Ni 18 Cr 10 Ni Cb SA178 Gr.C, Gr.D, SA192, SA210 Gr.A1

& Gr.C

SA106 Gr.B, Gr.C

SA209 T1 SA335 P12 SA213 T12 SA213 T11 SA335 P11 SA213 T22 SA335 P22 SA213 T91 SA335 P91 ---- SA213 TP304 H SA213 TP347 H 15 Mo3 13 Cr Mo 44 --- BS3059 P2 S2 360, 440 BS3602 P1 360, 430, 500 Nb --- BS3059 P2 S2 620 BS3604 P1 620 – 440 BS3604 P1, 621 10 Cr Mo 910 X 10 Cr Mo V Nb91 X 20 Cr Mo V 121 BS3059 P2 S2 622-490 BS3604 P1, 622 ---- ---- ---- BS3059 P2 S2 762 BS3604 P1 762 BS3059 P2 304 S51 BS3605 – 304 S59 E BS3059 P2 347 S51 BS3605 347 S59 E 482 535 552 577 635 700 704 704

DESIGN - CALCULATION OF THICKNESS REQUIRED IN VARIOUS CODES AREA IBR ASME SEC.I

Tube thickness Shell thickness Dished end thickness Flat end thickness PD + C 2f + P fE



PR + 0.75

0.5 P PDK + 0.75

2f d CP f + C PD 2f + P +0.005D

PR fE



(1



Y) P PR 2f



0.2 P d CP f PD 2f + P PR fE



0.5 P PDK 2f Cd P f BS 1113 DIN TRD 300 PD 2f + P PR fE



0.5 PE R 1+ 2P 2f



P



1 Cd P f

PIPING

•

Diameter and Thickness:

• The diameter of the piping is usually decided based on flow and heat transfer considerations.

In normal practice, the outside diameter is specified for procurement. These are based on the convenience and convention in manufacture.

After finalizing the diameter, the thickness of the piping is computed based on the imposed loads.

PIPING

• Diameter

– Based on flow requirements – Based on economic requirements – Based on size availability

PIPING

• Thickness

– Based on strength requirement – Based on process allowances – Based on thickness tolerances – Based on availability

PIPING

•

Fluids and Pressure Drop:

• The piping under present discussion may carry a single phase fluid or two-phase fluid. The following fluids are commonly handled by the piping: • • 1.

• 2.

Liquid Gas • 3.

• 4.

• 5.

Liquid-solid slurry Gas-solid mixture Liquid-vapor mixture.

PIPING

• Mixture of solids, liquids and gases are rarely used. In a maze of piping, flow distribution plays a major role in the design of piping. To calculate the flow in various branches of piping (in a maze of piping), the pressure drop in various branches are to be calculated.

The following formula is commonly used to calculate the pressure drop in a fully developed flow in a hollow circular pipe.

PIPING

• • • • • • •  f W 2 2gd L P = --------- • • • Where,  P = Pressure loss in terms of head, mm of fluid column f = Coefficient of friction g d W = Velocity of fluid, mm / sec.

L = Total length of pipe, mm = Acceleration due to gravity = 9806.65 mm/sec = Average inside diameter of pipe, mm 2

PIPING

• • • The following formula is commonly used calculate the pumping power required:  P p WA • HP = • • Where -------------- 75 x 10 9 • • HP = Pumping power, HP • p A = Density of fluid, gm/cc = Flow area =  d 2 / 4 Sq.mm

• • Example (Water at ambient temperature)

PIPING

• • • • • • • • • • • • • • •

HP Flow = 100 tonne / hr = 100 cu. m / hr = 100 / 3600 = 0.0278 cu.m / sec d = 102.26 mm (for 4” STD pipe =



114.3 x 6.02 mm x mm) W = 0.0278 / (



* 0.10226

2 / 4) = 3.38 m / sec = 3.380 mm / sec f L p



P = 100 m = 100,000 mm = 0.02 (approximate) = 1.0 gm / cc (for water at ambient temperature) = 0.02 * 3380 2 * 100,000 / (2 * 9806.65 * 102.26) = 11.392 mm water column



P p W A (11.392 mm wc) x (1.0 gm/cc) x 3.380 mm/sec) x (8.213 sq.mm) = --------------- = ------------------------------------------------------------------------------------- 75 x 10 9 75 x 10 9 = 4.22 HP. Considering a motor efficiency of 80%, motor rating = 4.22/08 = 5.28 HP.

Use a 6 HP Motor.

PIPING

•

Nominal Pipe Size (NPS):

• • The Nominal Pipe Size (NPS) in an ASME method of indicating the approximate outside diameter of the connected pipe in inches. Note that the unit (inch) is not followed after the designation.

• • •

Class of Fittings:

• The class of fittings is an ASME method of indicating the pressure carrying capacity of the fittings.

PIPING

• • • • •

I.

Pipe sizing and Pressure drop Calculations: Pipe Sizing:

Before proceeding beyond a preliminary / design of piping system, it is necessary to determine the pipe inside diameter which allow reasonable velocities and friction losses.

The maximum allowable velocities of the fluid in pipeline is that which corresponds to the permissible pressure drop from the point of supply to the point of consumption or is that which does not result in excessive pipe line erosion.

PIPING

•

Trade Practice Nominal ID.

– Steel pipes are designated by their OD or their

• •   § Due to manufacturing conditions, OD is constant.

§ Slight deviations from normal wall thickness, modify only the ID also called clear width.

• •   § Why a pipe is generally not referred to by its ID.

• •  § § Common Engineering practice to use nominal bore NB to indicate the proper size of the individual parts employed in a pipeline (pipes, flanges, fittings and valves).

Nominal bore = actual inside diameter.

PIPING

• •  •  § Pressure head (provided by booster pumps, compressors, natural head as in the case of gravity main).

•  § Pressure head is necessary for transmission to overcome losses in the flow rate due to internal friction in the moving fluid or to rough inside surfaces of pipe.

•  § available).

Selection of the diameter (flow rate anticipated pressure head § Pressure drop increased through turbulence and separation of flow of bends or in branch connections, fittings, valves and similar parts (reduce the economy of any pipe line.

PIPING

• • •

Velocity profile in Different System:

The mean velocities of steam and water in different system shall be as follows:

• • • • • • • • • • • • • •

PIPING

Q A d Where A =  A W  = --------- d 2 4 354025 x Qv = ------------------- w = Area, mm 2

PIPING

• • d • Q • • w = inside diameter, mm = flow rate, Tonnes/hr.

= Velocity, m/sec • • • • •   = Volume of medium, Kg/m

Pressure drop calculation:

3 The pipe sizes calculated based on the above recommended velocities do not relieve the designer to check the adequacy of pipe size from the flow friction consideration.

PIPING

•

Pressure drop calculations are of prime necessity in determining:

• • a) The selected inside diameter meets the available pressure drop in the case of main steam, cold reheat, hot reheat and auxiliary steam lines and miscellaneous water lines.

• • • b) The discharge pressure of the pump (boiler feed pump and condensate extraction pump).

PIPING

• For finding the frictional pressure drop in pipelines Darcy ’s Formula can be universally used for almost all the fluids.

With suitable restrictions for gases and vapours. As long as the pressure drop is around 10% of starting point pressure (which is true in most of the steam lines in thermal power station). Darcy ’s formula for pressure drop can be used since the specific volume change in the line due to pressure loss will have little effect on calculated pressure drop.

PIPING

• • • •

Calculation to determine the pressure drop in the pipe is made according to formula:

• • a) For straight pipe  flw 2 P = ---------------- kg/cm 2 • • • • • • • b)  20000 g c dv For bends, elbows, tees, valves, etc.

Kw 2 P = ---------------- 20000 g c v kg/cm 2

PIPING

• • • • • • • • • • Where, f= Friction factor found from a graph between Reynolds No. and Relative roughness.

K= resistance coefficient for fittings there are established based on experiments and are available in a standard table in various books.

l= length of pipe in meters V= velocity in m/sec g c = gravitational constant – 9.81 m/sec d= inside diameter of pipe in meter 2 v= specific volume in m 3 /sec.

PIPING

• • • • a)  P= Water (non-expansive flow) in compressible fluids.

l w 2 x   ---- x ----------- di 2g  h x  •  P= absolute pressure in lb/ft 2 • l= length of pipe line in ft.

• di= inside diameter of pipe in ft.

PIPING

• • w= velocity of flow in ft/sec  = specific gravity in lb/cu.ft (water = 62 lb/cu.ft) • g= acceleration due to gravity (=32.2 ft/sec 2 ) • • • h= geodesic height in ft for lines other than horizontal  = friction factor number dimension • • += ascending lines  = descending lines 0 = for horizontal lines.

• Pressure decreases in linear perspective with the length of the line, while the velocity remains unchanged.