BALANCE OF PLANT FOR THERMAL POWER PROJECT 2X500MW WATER TREATMAENT PLANT

By: Abdullah

1.Water is a key Input required for Thermal Power Generation

2.Available water resource are fixed an water requirement is increasing

3.Water has priority for drinking & irrigation over that for power generation

4.Availability & Allocation of water for Thermal power plant has been reducing

5.Low grade water is also being supplied as input Raw water to the Thermal plant

Water Availability Aspect

1.Clarified water as cooling tower make-up and service water

 

2.Demineralisd water for heat cycle make-up, equipment cooling system make-up, condensate polishing plant regeneration etc.

 

3.Filtered & disinfected water for potable water requirement.  

BOP Comprises1.Plant Water System 2.Cooling Water System3.Coal Handling System4.Ash Handling System5.Mechanical Auxiliaries (Fuel Oil, Fire Fighting, AC, Ventilation etc,)6.Plant Electricals7.Contorl & Instrumentation8.Civil Structural & Architectural works

Typical Water Uses In Coal Based Thermal Power plant

1.Cooling of condenser & secondary cooling of PHES in ECW system

2.Power cycle make up

3.Wet Ash Disposal

4.Coal Dust suppression

5.Air conditioning & Ventilation

6.Other uses viz potable uses, plant washing

Cooling Water System

Once through system:Permissible for coastal site with temperature rise of 7 deg c over temperature of receiving water body

Closed cycle open recirculation system using cooling tower:Required make up water to compensate for loss of water due to evaporation , drift and blow down

Blow down is required to maintain a desired level of COC in CW system

CT Make –Up & Blow DownCT make –up water, M=E.C/C-1

Blow down water, B=E/C-1-D

Where

E=Evaporation

D=Drift

C=COC of CW system

Features of Plant water Requirement1.Source / quality of raw water

2.Type of CW system

3.Quality of coal

4.Plant design aspect

5.Uses of dry fly ash

6.Treatment /Reuse of waste water

Earlier water was taken as an assured input

Plant consumptive water with Cooling tower used to be about7meter cube /h/MW without ash water recirculation

And 5meter cube /h/MW with ash water recirculation

Consideration For Reduction Of Plant Water Requirement

1.Clarifier sludge water and filter backwash to be recycle

2.COC of 5 for CW system operation

3.Boiler Blow down to be used as part of CT make-up

4.Power cycle make up as 2% of BMCR flow

5. Waste water to used for coal dust suppression and gardening

6.Dry cooling system as per constraint in availability of raw water

Consideration With Dry Cooling System

Condenser cooling by dry cooling system

ACW(Auxiliary Cooling Water) system to be based on wet cooling tower

Fly ash disposal in dry mode/ HCSD mode

Bottom ash disposal in Wet mode

Water Treatment system

Water Balance Diagram 2x500MW Coal Based TPP With Dry Cooling System

Water Balance Diagram 2x500MW Coastal TPP

Wet Cooling System: 3.6meter cube/h/Mw during initial period of plant operation with fly ash disposal in wet mode Dry Cooling System:0.75 meter cube/h/MW during initial period of plant operation without recovery of bottom ash waterCoastal plant:Fresh water requirement 0.4 meter cube/h/MWSea water to be used for process cooling & ash disposal

Direct Dry Cooling:- Air Cooled Condenser LP turbine exhaust steam is directly cooled inside a system of finned

tube bundles by ambient air using forced draft fans No Terminal Temperature Difference(TTD) is involved

Indirect Dry Cooling:-Surface condenser Steam is cooled in a surface condenser by circulating water which in

turn, inside a system of finned tube bundles is cooled by ambient air using fan or a natural draft tower

Terminal Temperature Difference (TTD) is involved

Air Cooled Condenser With Fan

Indirect Dry Cooling With Surface Condenser

Jet Condenser

Hybrid condenser

Plant Water System

DESALINATION

It is a process that removes or separates salts from saline water to give fresh water, at the expense of energy.Depending upon the type or form of energy used, Desalination Processes can be broadly classified into two groups:1. Thermal Desalination2. Membrane Desalination

Multi-Stage Flash (MSF) Distillation

Typical raw water analysis considered for canal water is as under:  

S. No. Constituents Concentration     i) PH 8.2     ii) Conductivity, micro mhos/cm 450     iii) TDS 315     iv) Turbidity, NTU 20-500     

v) Calcium hardness as CaCO3 ppm 110     

vi) Magnesium hardness as CaCO3 ppm 95     

vii) Sodium as CaCO3 ppm 100     

viii) Potassium as CaCO3 ppm 10     

ix) Total cations as CaCO3 ppm 315     

x) P-Alkalinity as CaCO3 ppm Nil     

xi) M-Alkalinity as CaCO3 ppm 250     

xii) Chloride as CaCO3 ppm 30     

xiii) Bicarbonates as CaCO3 ppm 250     

xiv) Sulphate as CaCO3 ppm 25     

xv) Nitrate as CaCO3 ppm 5     

xvi) Floride as CaCO3 ppm 5     

xvii) Total Anions as CaCO3 ppm 315     

xviii) Dissolved silica, mg/l as SiO2 8

•Typical consumptive requirement at COC of 5 for 2 x 500 MW thermal project is as under:

S. No. Description Requirement, m3/h

1 Cooling tower make up 2550*

2 DM water 85

3 Potable water 52

4 Service water 200

5 Reservoir evaporation 30$

6 Loss in sludge etc. 2

7 Bottom ash system make up 90#

  Total 2899 say 3000

THERMAL DESALINATION

Thermal desalination processes involves heating of saline water to its boiling point to produce water vapor, this pure vapor is condensed to produce fresh water.The three types of thermal desalination units used commercially are:1. Multistage flash (MSF)2. Multiple effect distillation (MED)3. Low Temperature Evaporation (LTE)

Multi-Effect Distillation (MED)

Low Temperature Evaporation

MEMBRANE DESALINATION

Membrane processes use a semi permeable membrane to move water across the membrane from the salt solution to produce fresh water on the other side of the membrane.

Membrane desalination is classified depending on the driving force.Process Size of materials

retainedDriving force

Microfiltration 0.1-10.0 microns molecules

Pressure difference

Ultrafiltration 5-100 nm molecules Pressure difference(1 - 4 bar)

Nanofiltration 0.5 - 5 nm molecules (mostly charged species)

Pressure difference(5 - 15 bar)

Reverse Osmosis < 1 nm molecules Pressure difference(10 - 60 bar)

MICROFILTRATIONMicrofiltration is a process of separating material of colloidal size and larger than true solutions. The MF membranes are made from natural or synthetic polymers such as cellulose nitrate or acetate, polyvinylidene difluoride (PVDF), polyamides, polysulfone, polycarbonate, polypropylene, PTFE etc. The inorganic materials such as metal oxides (alumina), glass, zirconia coated carbon etc. are also used for manufacturing the MF membranes.Applications of MF are:1. Food & beverages2. Chemical industry3. Microelectronics industry4. Fermentation

ULTRAFILTRATIONUltrafiltration is most commonly used to separate a solution that has a mixture of some desirable components and some that are not desirable. Rejected species include sugars, biomolecules, polymers and colloidal particles.Applications of MF are:1. Oil emulsion waste treatment2. Treatment of whey in dairy industries3. Concentration of biological macromolecules4. Electrocoat paint recovery5. Concentration of textile sizing6. Concentration of heat sensitive proteins for food additives 7. Concentration of gelatin 

NANOFILTRATIONThe separation mechanism of NF involves size exclusion as well as electrostatic interaction. In NF, organic molecules with molecular wt. greater than 200-400 are rejected. Membranes used for NF are of cellulosic acetate and aromatic polyamide type.Applications of NF are:1. Concentration of sugars, divalent salts, bacteria, proteins, particles, dyes and other

constituents that have a molecular weight greater than 1000 daltons.2. Removal of color and total organic carbon (TOC) from surface water3. Removal of hardness from well water4. Overall reduction of total dissolved solids (TDS)

REVERSE OSMOSISRO membranes give 96%-99% NaCl rejection. Greater than 95-99% of inorganic salts and charged organics will also be rejected by the membrane due to charge repulsion established at the membrane surface.RO membranes are made of polymers, cellulosic acetate and aromatic polyamide types.Applications:1. Potable water from sea or brackish water2. Ultra pure water for food processing and electronic industries3. Pharmaceutical grade water 4. Water for chemical, pulp & paper industry 5. Waste treatment etc.6. Municipal and industrial waste treatment

MEMBRANE PREPARATION

Membrane preparation was done using the immersion precipitation technique.

Dry polysulfone beads were taken in air tight bottles and then a specific amount of DMF was added to dissolve the polymer. The same method was applied the PVDF powder.

A piece of fabric was kept on the glass plate and the casting solution was spread on it evenly.

The entire assembly was immediately immersed in a room temperature gelling bath made by using Ultra Filtered water.

The membranes were stored in laboratory refrigerator maintained at 5oC.

Renewable Energy based Desalination

Conventional sources of energy are depleting fast and hence there is an urgent need to find renewable sources of energy. Desalination can also be carried with the help of renewable sources of energy such as solar energy. One of the methods is Solar Reverse Osmosis. This setup can also be done in those areas where access to grid electricity is not possible. Also, renewable energy based methods are pollution free and environmental friendly.Solar Reverse Osmosis Unit:•POWER PACK•PRE-TREATMENT•REVERSE OSMOSIS MEMBRANE•POST TREATMENT

PIPE PRESSURE DROP CALCULATIONS

Factors affecting pressure drop calculations:1. Friction between the fluid and the wall of the pipe2. Friction loss as the fluid passes through any pipe

fittings, bends, valves, or components3. Pressure loss due to a change in elevation of the fluid

(if the pipe is not horizontal)4. Friction between adjacent layers of the fluid itself

ELECTRICAL AND CONTROL & INSTRUMENTATION SYSTEM

Electrical System - Design Criteria :

11kV/ 3.3kV incomers from station switchgears to 11kV/ 3.3kV station auxiliary plant/system switchgear shall be through adequately rated cables. 3.3kV switchgear shall befed from transformer either through cable or busduct. For 415V system, busduct shall beused for incoming connection from transformers to the switchgear wherever transformerrating is 1000kVA and above.

Electrical System - General Technical Requirements :

1.Transformers

The transformers shall be provided with delta-connected primary and a star–connected secondary with the star point brought out and resistance earthed for 3.3kV system and solidly earthed for 415V system.

2. 11kV and 3.3kV Busducts :

a) Number of phase 3 3b) Frequency 50 Hz 50 Hzc) Nominal voltage 11kV 3.3 kVd) Highest system voltage 12 kV 3.6 kVe) One minute power frequency withstand voltage (dry and wet) 28 kV 10 kVf) Impulse voltage withstand value with 1.2/50 micro-sec wave shap 75 kV 40 kVg) Continuous current rating as required as requiredh) Short time current rating for 1 second 40kA 40kAi) Dynamic current withstand rating 100 kA(peak) 100kA(peak)j) Type of cooling Natural Naturalk) Type of bus enclosure Phase segregated Phase segregated

2. 11kV and 3.3kV Switchgears:

The switchgears shall be indoor, metal clad, draw out type. The motor feeders above

2000kW rating shall have vacuum/ SF6 breakers. The motor feeders below 2000kW

rating shall have either vacuum/ SF6 breakers or vacuum/ SF6 contactors backed up by

HRC fuses. However, in an application, where frequent start/ stop operations are

required, vacuum contactors/ breakers shall be preferred. The operating mechanism of the

circuit breakers shall be of the stored energy type DC motor operated charging springs.

3. DC System :DC system comprising of DC storage batteries suitably rated Trickle and Boost chargersand DC distribution boards shall be provided to cater the normal DC loads.

4. Power and Control cables and Laying & Termination :For 11/ 3.3kV system, Power cables shall be XLPE insulated with conductor and insulation screens armoured and FRLS PVC outer sheathed.

Fire alarm, annunciation and protection system. DC supply cables to switchgears. DC cables from batteries to DC boards. DC emergency lighting cables for main building etc.

5. Lighting system:The auxiliary building shall be provided with

a) Main Lighting systemb) Emergency lighting systemc) Minimum emergency lighting systemd) Suitable no. of Portable lighting units

6. Earthling and Lightning Protection system: Earthling and lightning protection for the entire areas or buildings covered shall be provided in accordance with IS 3043, IS 2309, IEEE 80 and IEEE 665 and Indian Electricity Rules/ Acts.

3. Control & Instrumentation System - Design Criteria : A totally integrated instrumentation and control system covering the total functional requirements of

sequential control, interlock, protection, monitoring, alarm, data logging, fault analysis etc.