Calculation of power generation cost of Thermal power plants & Co-generation plants

Power generation cost: It is the amount of rupees spent on generation of 1 unit of power

Power export cost: It is the amount of rupees spent on export of 1 unit of power

Generally power generation actual cost is the sum of Fuel cost, man power cost, operation & maintenance costs administration cost, river water cost, plant gardening & vehicles cost  etc

Power generation & Export cost in Thermal power plants:

Part A:Fixed data

• Total power generation in KWH = A1

• Total power export KWH = A2

• Total fuel consumed = A3

• Rate of per ton of fuel in = A4

• Raw water consumption per day in MT or M3 = A5

• Rate of per ton or   of river water in  = A6

• Rate of per unit power for lifting water from source to Reservoir Rs= A7

Calculation of power generation in steam Turbines

Part B:

Operation cost head wise

• Cost of fuel in Rs B1= A3 X A4

• Cost of raw water in Rs B2 = A5 X A6

• Cost of chemicals consumed for water treatment = B3

• Cost of fuel feeding in =B4

• Cost of raw water lifting charges from river to reservoir= B5

Total operation cost C = B1 + B2 +B3 + B4 + B5

Power generation phenomenon in STG

Part C:

Maintenance cost head wise

• Cost of spares,consumables consumed  = C1

• Cost of Lubricants = C2

• Cost of store inventory= C3

• Tools tackles testing cost = C4

• Measuring instruments calibration cost = C5

Total maintenance cost C = C1 +C2 + C3 + C4 + C5

Part D :

Administration cost head wise

• Cost of  O &M man power salary = D1
• 
  
• Cost of site expenditures =  D2
• 
  
• Cost of gardening labours salary =D3
• 
  
• Cost of Security guards salary = D4
• 
  
• Cost of transportation vehicles =D5

Total administration cost = D = D1 + D2 + D3 + D4 + D5

• Total Cost of production, E = B + C + D
•  
• Power generation cost per unit =A1/E....Rupees/KWh or Dollars/Kwh
• 
  
• Power export cost per unit = A2/E.....Rupees/KWh or Dollars/Kwh

Note:

1-In calculation power generation cost, power consumed for plant auxiliary running should not be considered

2-In co-generation plants:

• Cost of power given to process plants should be considered
• Cost of process steam given should be considered for power generation cost calculation

Read

Power Transformers QnA

How to calculate the cost of steam???

Power plant: Water sources & impurities present in it.

Water is basically the combination of 2 parts of Hydrogen & 1 part of Oxygen. It is very impossible to get pure water in the nature . Pure water does not exist in nature due to its characteristic as solvent. Number of matters like gases, minerals and organic materials dissolve in the water easily.

Water mixes with  fine particles wherever it flows such as silt, sand, iron,mud & organics etc. Biological growths like algae & bacteria take place in the water. Thus, water is usually contaminated with dissolved & un-dissolved solids along with living matters!

Raw Water sources in nature:

• Rain water:
• Surface water:Rivers, Streams, Ponds, Lakes, and Reservoirs
• Ground water :Springs, Shallow Wells and Deep Wells

For Boilers, heat exchangers ,domestic & other industrial purpose, we cannot use these above water directly from their sources.Before using it, need to carryout some treatment to get required quality for particular application. water being universal solvent has lot of impurities int it.

Rain water is said to be very purest form of water, but after falling on ground it mixes with river, lake,seal water & soil, which makes it impure & unsuitable for direct use.

Effects of impure or raw water :

• Scales in Boilers and Heat exchangers.

• Poor quality boiler steam.

• Corrosion of boilers, heaters and piping.

• Stains, discoloration, spots.

Impurities present in water:

• Dissolved impurities also called as Ionic impurities

• Undissolved impurities also called Non-ionic impurities

• And Gaseous impurities

1-Dissolved or Ionic impurities:

These are again divided into Cationic & Anionic

Cat ionic dissolved impurities

• Magnesium
• Calcium
• Sodium
• Potassium
• Iron
• Mangnese

Calcium and magnesium are the most common dissolved impurities found in water. When calcium and magnesium salts are present in considerable amount it imparts hardness to water i.e. it does not allow lather to form with soap. 

The salts of calcium and magnesium causes temporary (Carbonate) & permanent hardness (Non carbonate).

Sodium & Potassium are always present in any kind of water, but they will not harm much if the percentage of concentration of these salts are less.

Iron present in the water can cause corrosion & clogging. Iron can be in dissolved & precipitated form.

An ionic dissolved impurities

• Chlorides
• Sulphates
• Nitrates
• Phosphates
• Silica.
• Bi carbonates
• Carbonates
• Hydroxide
• Fluorides

Chlorides: can be found  in all kind of water. The chloride  may be in combination with one or more cations, calcium, magnesium, iron and sodium. Chlorides of these salts are present in water because of their high solubility in water. 

Excessive chloride in water causes corrosion. It also impart taste to water. Chlorides are prominent in crevice corrosion and pitting.

Sulphates: Most raw water contains sulphates due to leaching and erosion of sulphate minerals and oxidation of sulphides. They can also be due to industrial waste discharge and farm drainage.

 Sulphate also occur due to aerobic oxidation of organic matter. Sulphate in water causes corrosion and scaling in boiler. Sulphate are normally found as calcium, magnesium and sodium salt. Sulphate are also aggressive to concretes.

Silica:Most natural water contain silica up to 100  ppm. Silica is an oxide of silicon which is a major constituents of igneous and meta morphic rocks, of clay minerals.Silica can exist in various form as simple silicates or as a complex polymeric material. Colloidal silica is rarely present in Bore well water but is commonly present in surface water. 

Silica can cause deposits on boiler, cooling tower, turbines ,pipe lines etc

2-Undissolved non ionic impurities:

These include

• Colour
• Taste and odour
• Turbidity or suspended solids.
• Oil.
• Organic matter
• Colloidal silica

Colour: is normally expressed in Hazen units and is caused by the presence of colloidal suspension and aquatic growth. It is also caused by dissolved organic substance due to decomposition of vegetation. Some water may have colour due to presence of iron.

Turbidity is caused by the presence of suspended solids in water. It is a measure of total weight of dry solids present whereas turbidity is an optical effect. The suspended impurities include clay, sand, algae and precipitated iron.

Taste and odor: Organics and some inorganic chemicals present in the water contribute taste and odour. These chemicals can originate from municipal or industrial waste or from natural resources such as decomposition of vegetable matter.

Organic impurities: Organic impurities can be due to vegetable decomposition. It is also due to organic matter which comes from animal and human fecal matter or it’s degradation products, industrial waste and agriculture pesticides and herbicides.

3-Gaseous impurities:

 Gaseous impurities mainly include

• Carbon di-oxide,
•  Oxygen,
• Hydrogen sulphide,
• Ammonia
• Chlorine.

Carbon di-oxide: Surface water contains small amount of free CO2 but well water may contain more than 100 ppm as Carbon-di-oxide is found in waters coming in contact with decaying organic matter or carbonaceous material.

Depending on the pH of water carbon di- oxide may be present either as free carbonic acid (dissolved CO2 gas) or in a semi carbide form (as bicarbonates) or in a combined form (as carbonates), free CO2 depresses the pH and thus accelerates corrosion.

Oxygen: is practically absent in natural water, but is usually present in surface waters rather in high concentration. Oxygen is corrosive to metals but its  absence in natural waters could produce other obnoxious gases such as methane H2S etc.Dissolved oxygen is highly corrosive and should be removed either chemically or mechanically especially in Boiler feed water.

Hydrogen sulphide: is found in some well waters in areas where the soil contains certain types of organic matter, decomposing under anaerobic conditions .H2S creates unpleasant odour to water, promoters metal corrosion and  causes  clogging of pipes. 

Ammonia: is  due to industrial and agricultural pollution. It is corrosive to copper and brass at pH 9.0. Ammonia can be removed by various methods-Deaeration, chlorination or by hydrogen cation exchange if in ionic form.

In order to safeguard the Boiler, heat exchangers & pipe lines, it is utmost important to carryout the water treatment process to get required quality of water as feed water,cooling water etc.

Water treatment is divided into

Internal treatment: This treatment is done in Boiler drums, cooling water etc

External water treatment : It is carried out out side the unit (Boiler, Cooling water)

External water treatment process includes following sequential  sub processes & systems

• Sedimentation: Normally happens in water reservoirs

• Clarification: Removes turbidity , kills microorganisms

• Filtration: Involves multi grade filters to remove turbidity

• Ultra-filtration: Process of bringing down the water turbidity to <0.2 NTU

• Reverse osmosis process: Removes reactive silica & conductivity

• De-mineralisation: Removes Cation & Anion impurities present in water

Water treatment plant chemicals and their functions

WTP CHEMICALS
SL NO.	CHEMICAL NAME	FUNCTION	APPLICATION
1	Sodium Hypochlorite	To kill microorganisms (bacteria. Algae and other germs)	Clarifier
			Ultra Filter (UF)
			Cooling tower
2	Ferric chloride	Coagulation	Clarifier
3	Polyelectrolyte	Flocculation	Clarifier
4	Hydrochloric acid	Regeneration by cation exchange	Regeneration of SAC, MB
		Membrane cleaning	UF & RO Membranes
5	Caustic soda lye	Regeneration by anion exchange	Regeneration of SBA, MB.
		Membrane Alkali Cleaning	UF
6	Caustic flakes	Regeneration by anion exchange	Regeneration of SBA, MB.
7	Trisodium phospate	Sludge Conditioner & Corrosion inhibitor	Boiler steam drum Drum (Through HP  dosing pump)
8	Hydrazine Hydrate	To remove Oxygen	1-Deaerator outlet feed water line (Through LP dosing) 2-Boiler Wet Preservation
9	Morpholine	pH boosting	Deaerator outlet feed water line (Through LP dosing) 2-MB outlet 3-Boiler Wet Preservation
			MB outlet
			Boiler Wet Preservation
10	Antiscalant	Prevention of scale	RO Membranes
11	Sodium Meta bisulphite	To reduce chlorine	RO Membranes
12	Biocide	Reduce Algae, bacteria & fungi growth	RO Membranes cleaning
13	Acidic cleaner	Salts removing	RO membranes
14	Alkaline Cleaner	Salts removing (Cleaning inorganic scales)	RO membranes
15	Scale inhibitor	Prevents scaling	Cooling Tower
16	Corrosion  inhibitor	Prevents Corrosion	Cooling Tower
17	Bio-Dispersant	Bio-Dispersion	Cooling Tower
18	Non oxidising Micro Biocide	To kill microorganisms	Cooling Tower
19	Non oxidising Micro Biocide	To kill microorganisms	Cooling Tower
20	Sulphuric acid	To maintain pH (To reduce Alakalinity of water)	Cooling Tower
21	Chlorine Granuals	Bacteria killing	Cooling Tower
22	Zinc base chemical	To prevent corrosion of Copper base alloy	Cooling Tower
23	Oxidising Biocide (Chlorine activator)	Controls biofouling in heat exchangers like Condensers, oil coolers)	Cooling Tower

Boiler HP dosing system capacity calculation

Shaft couplings & selection guide

A shaft coupling is a mechanical device used to connect rotating shafts and absorb misalignments between them. A coupling is a mechanical device, which is used to connect driver and driven shaft permanently or semi permanently.

Couplings can be rigid or flexible depending on the alignment accuracies of the system and torque requirements. Shaft couplings are used for power and torque transmission between two rotating shafts such as on motors and pumps, compressors, and generators.

Functions of couplings:

• Connects the shafts of two units, which are manufactured separately.
• Transfers motion, power and torque
• To reduce transmission shock loads from one shaft to another
• Protection against overloads.
• Introduces mechanical flexibility.

Design considerations for couplings:

• Type of drive & driven equipments
• Alignment accuracy
• Operating & surrounding temperatures
• Type operation (Intermediate, continuous, frequent ON/OFF etc)
• Shafts diameters to be connected
• Maximum & minimum bores size
• Operating & design power
• Maximum & peak loads
• Space available
• Operation & Maintenance cost
• Service factor (Generally, for medium duty use a service factor of 1.5. For heavy duty use a factor of 2 and for extra heavy duty a factor of 3 should be used)

Types of couplings:

Main types of couplings: Rigid coupling and Flexible coupling

Regid couplings:

Rigid coupling is used to connect two shafts which are perfectly aligned. Most of the rigid couplings are made of aluminum, steel, or stainless steel.

Types of Regid couplings:

• Sleeve or muff coupling
• Clamp/compression
• Flange coupling

Considerations for regid coupling selection:

• Angular misalignment tolerance
• Parallel misalignment tolerance
• Axial motion allowed
• Dimensions like Bore diameter,Coupling diameter,Coupling length & Design units

No.of coupling bolts for flange couplings

• 3 if shaft size is up to 40 mm

• 4 if shaft size is 40–80 mm

•  6 if shaft size is 80–180 mm

Flexible Couplings:

• Pin bush coupling (Protected and unprotected type)

• Jaw/spider/love joy coupling

• Gear coupling

• Bibby/grid coupling

• Metaflex/flexible disc coupling

• Tyre coupling

• Fluid coupling

• Oldham’s coupling

Dimensions available Pin bush coupling catalogues:

• Coupling size

• Coupling flange diameter

• Hub diameter

• Coupling gap

• Coupling maximum & minimum bore diameters

• No.of pins or bolts

• Maximum speed

• Torque

Gear Couplings:

Gear couplings also transmit high torques. They have misalignment capabilities generally about 0.01-0.02 inch in parallel and 2 degrees in angular. Gear couplings are often used in pairs with spacer shafts to span the distance between the driving and driven equipment. They generally require lubricant although some designs intended for lighter duty use lubricant free nylons or other polymers for the center sleeve.

Grid Couplings:

Grid couplings employ spring-like connecting elements that weave between slots machined in the coupling hubs. They are capable of high torque transmission with an added bonus of shock absorption and torsional vibration dampening. They operate without lubricant. They are appropriate for power transmission and capable of handling parallel misalignment up to 0.30 inch and angular misalignment of about ¼ degree.

Disc Couplings:

Disc couplings use single or multiple discs and single or double stages which bolt to the shaft hubs. They are used for power transmission and rely on the flexibility of their thin metal discs to transmit torque and accommodate angular misalignment. They are not especially good at managing parallel misalignment. They are capable of transmitting high torques and are often used to couple high horsepower motors, gas turbines, etc. to loads.

Oldham Couplings:

Oldham couplings handle high degrees of parallel misalignment owing to their sliding element design. Use of an elastomer center element instead of metal is popular in modern versions. Some manufacturers claim an ability to tolerate up to 5-degree angular misalignment through the use of cylindrical, rather than rectangular, sliders.      

Fluid Couplings:

Fluid couplings or hydraulic couplings work on the hydrodynamic principle. In drives consisting fluid couplings, there is no mechanical contact between the driver and the driven machine and power is transmitted by means of a fluid. Due to the mechanical separation between the driver and the driven machine, a fluid coupling enables to achieve two separate value of acceleration in the drive, the fast value of acceleration for the driver and simultaneously the slow value of acceleration for the driven machine. 

         Fluid couplings are often used to drive large inertia machines in combination with squirrel cage motors. They permit a load free acceleration of the motor and consequently with increasing oil fill, provide a soft/gentle quasi steady state start-up of the machine. The maximum torque occurring during the start-up process is restricted to lowest possible level. As fluid coupling allows quick acceleration of the motor and short duration of high value starting current, it results into economical design for electrical system. In addition, systems that use multiple motors can be switched on in a staggered sequence to limit the current demanded during the motor acceleration. This avoids grid overloading caused by simultaneous motor starts.

Fluid couplings are used in drives for conveyor systems such as belt conveyors, bucket elevators and chain conveyors. The smooth application of fluid coupling torque provides a smooth start-up of belt conveyor to protect the belt from damaging stresses. In heavy industry, they are used for applications such as crushers, roller presses, mixers, large ventilators, boiler feed pumps, large compressors, centrifuges, etc

Types of fluid couplings:

Constant fill type:

Constant-fill Couplings Couplings of this type are mainly used for start-up (to limit torque) and to cushion the torsional vibration of the drive chain. In this type of couplings, various designs mainly differ through adjoining chambers, who’s automatically controlled filling and emptying have a significant influence on the start-up behavior. Constant-fill couplings are sealed to the outside. Filling of the operating fluid in a coupling is carried out before its commissioning.

Drive requirements determine the design and filling quantity. The ratio of the operating fluid volume filled to the overall volume of the coupling is called the fill level.

Variable-speed Couplings:

Couplings of this type are used to control or regulate the speed of the driven machine over a wide range below the drive speed. These couplings have devices that seamlessly change the transmission behavior during operation. This mainly occurs by changing the fill level. The fill level can be changed during operation either via a radially movable scoop tube or by controlling the operating fluid inlet and outlet via valves and nozzles. These couplings always have an external fluid circuit for filling changes that can also aid cooling.

Missalignment tolerances for angular & parallel alignments

Speed (RPM)	Angular misalignment in Mills/inch of coupling diameter		Parallel misalignment Mills
	Good	Acceptable	Good	Acceptable
600	1	1.5	5	9
900	0.7	1	3	6
1200	0.5	0.8	2.5	4
1800	0.3	0.5	2	3
3600	0.2	0.3	1	1.5
7200	0.1	0.2	0.5	1

Calculations:

Example-1:What is the size of muff coupling, which is required to fit on 50 mm shaft Outer diameter of muff or sleeve = 2 X shaft diameter + 13 mm

                                            = 2 X 50 + 13 = 113 mm

                Length of sleeve = 3.5 X shaft diameter =3.5 X 50 =175mm

Example-2: Calculate the flange coupling dimensions required to fit on a shaft of 65 mm diameter.

Based on shaft diameter we can calculate the following dimensions of flange coupling.

Outside diameter of hub = 2 X shaft diameter (d) ==2 X 65 = 130 mm

 Length of the hub = 1.5 X d = 1.5 X 65 = 97.5 mm

Pitch circle diameter (PCD) of the bolts = 3 X d = 3 X 65 = 195 mm

Outside diameter of the flange = 4 X d = 4 X 65 = 260 mm

Thickness of flanges = 0.5 X d = 0.5 X 65 = 32.5 mm

Example-3:What is the maximum torque developed on a gear coupling mounted for pump & motors of power rating 525 KW & speed 3000 RPM

Torque = 9550 X Power/Speed

         T = 9550 X 525/3000

         T = 1671.25 Nm