Role of SWAS in

Cogeneration plants

SWAS(Steam and water quality analysis system)

Cogeneration plants

J P MUKHERJI & ASSOCIATES PVT

LTD

M. S. Sundaram, S. Parthasarathy,

Ms J. R. Chitre, Parag Gaikwad

• Boiler feed water & outlet steam need monitoring for conditioning.

• Poor quality of feed water & outlet steam

Why SWAS ?

• Poor quality of feed water & outlet steam creates serious problems in Steam Generator and Power Turbine even leading to blackouts .

Results of poor steam quality on

turbines

• Deposition on turbine blades • Corrosion fatigue of blades, discs• Particle erosion • Wheel chamber pressure increases• Sticking Emergency valve stems • Plugging of seals

Silica deposition on Turbine

blades

Silica and Sodium damage on

Turbine blades

Case I - Problems due to

poor water quality

New 12.5 MW, 67bar co-gen plant with newwater treatment plant installed in western India.Silica analyser not working in SWAS panel. In fullscale production during first season, lower poweroutput higher steam demand noticed. Plantoutput higher steam demand noticed. Plantstopped and silica coating on turbine bladesobserved. Plant was down for 3 weeks. Bladescleaned and rotor reinstalled. Repair Rs.1,500,000 (25000USD) & also loss in powerexport. Total loss more than Rs. 5,000,000(83000USD) .

Case II - Problem due delay in

Analysis

3500TCD plant, south India, 110 bar, 22MWturbine, 16MW export. Silica analyser notworking from start. (Problem in sampling) Onenight shift report on HP dozing delayed. Nextnight shift report on HP dozing delayed. Nextmorning high levels of sodium phosphate indrum sample. Corrections implemented butpower reduced two days later. Turbine runcontinued at lower export for another week andstopped. Silica and sodium noticed on blades.

Case II - Continued

Turbine experts cleaned rotor by sand blastingand then reassembled and balanced theassembly. Since shut down was towards end ofseason, little production lost. Mainly powerexport loss of Rs. 11,800,000 (0.2million USD).export loss of Rs. 11,800,000 (0.2million USD).User chemists competent, silica analyser still notworking in SWAS panel .

Case III - Problems due to

condenser tube leak

• US combined cycle power plant- operated intwo shifts . High Cation Conductivity readings ofcondensate ignored by oversight.condensate ignored by oversight.

• High reading due to minor leak in condensertubes . Problem detected three weeks later dueto major feed water contamination . Turbinestopped

Case III - Continued

Sodium coating on turbine . Plant shut down for3 months Repairs and power production lossesamounted to millions of USD. Example citied bypower consultant in “Power” magazine 2010 tostress Cation Conductivity importance.stress Cation Conductivity importance.

Introduction to SWAS

• SWAS is essentially an early warning systemwhich monitors the critical parameters in thePower Cycle. SWAS receives samples,conditions them & finally provides analysis togive a correct scenario of what is happening inthe Power Plant.the Power Plant.

• It has mainly two parts

1. Wet panel2. Dry panel

Typical Parameters analysed in

SWAS

1. pH

2. Conductivity, Cation conductivity3. Silica3. Silica4. Dissolved oxygen5. Sodium6. Hydrazine / Amine

Requirement of pH Measurement

Corrosion in a boiler is very pH dependant. ThepH value of feed water directly gives indicationof Alkalinity or Acidity of this water. It is normalpractice to keep the pH value of feed waterslightly Alkaline (9-9.5)

Typical system used: pH combination electrodewith coupled electronics.

Requirement of Conductivity

Measurement

• Conductivity is an important parameter fordetecting any contamination of steam since anydissolved impurity will raise conductivity instantly.Conductivity of all Cogen samples lies betweenConductivity of all Cogen samples lies between0.1 to 10 µsiemens/cm

• Typical system used : Conductivity cell -2electrode type, flow-thru cell with coupledelectronics Electrodes could be SS, graphite,titanium etc

Requirement of Cation

conductivity measurement

• Conductivity of sample after passing throughstrong Cation resin bed.

• Always measured in addition to specificconductivity.conductivity.

• Best method to detect contamination of feedwater and steam .

• Also of great use in detecting condenser leaks.• Cation conductivity should be low in feed water

steam and condensate <0.2µsiemens/cm

Requirement of Silica

Measurement

The solubility of silica in steam increases withpressure leading to chances of Silica carryover.The carryover of Silica leads to deposition onsuper-heater tubes & Turbine blades, whichcauses loss of efficiency & failure of Turbine.causes loss of efficiency & failure of Turbine.Ideally silica level in steam should be<20ppb.

Typical system used: Silica-colorimetricanalyzer - Molybdenum blue method

Requirement of Dissolved

Oxygen Measurement

At high temperature, especially with elevatedconductivity, oxygen reacts readily with mostmetals. This corrosive attack not only weakenssystem components but also results in sludgewhich can deposit on heat transfer surfaces &which can deposit on heat transfer surfaces &turbine blades. Control of dissolved oxygen isextremely important in any boiler cycle. Level infeed water expected less than 20ppb

Typical system used: Membrane electrode withcoupled electronics

Corrosion Effect in Boiler tubes

due to Dissolved Oxygen

Requirement of Sodium

Measurement

The presence of Sodium signals indicatecontamination with potentially corrosive anionse.g. Chlorides, Sulphates etc. At high pressure& temperature neutral sodium salts exhibitconsiderable steam solubility.considerable steam solubility.Sodium levels should be same in steam andturbine condensate <5ppb.

Typical system used: Ion selective electrodewith associated electronics

Requirement of Hydrazine

Measurement

• Hydrazine is chemically known as N2H4 , and isa powerful reducing agent used in boiler feedwater treatment as an oxygen scavenger andmetal passivator.

• Excess Hydrazine to be avoided as it is costly &also leads to copper contamination in boiler

• Typical system used: electrochemical, 3electrode amperometry with associatedelectronics

Typical SWAS Streams

Feed Water Sp. Cond., Cation cond.,Silica, DO2, pH, Hydrazine

Boiler drum pH, Sp. Cond., Silica, Boiler drum pH, Sp. Cond., Silica,

Superheated Steam

pH, Sp. Cond., Cation cond., Silica, Sodium

Condensate pH, Sp. Cond., Cation cond., Silica, Sodium

Main superheated steam header (Based on IS 14199:1995 & Hach guidelines)

pH 9.0 to 9.4

Specific Conductivity <10µS/cm

Cation Conductivity <0.3µS/cm

Silica <20ppb

Sodium <5ppb

Steam quality desired by

Turbine OEM

Silica <20ppbSodium 5 to 20ppb

Chloride 3 to 15ppb

Sulphate 3 to 15ppbSulphate 3 to 15ppb

Specific Conductivity 3 to 5µS/cm

Cation Conductivity (Desired)

0.1 to 0.3µS/cm

Cation Conductivity (Actually achieved)

0.2 to 2.0µS/cm

Turbine condensate (Based on IS 10496-1994 & Hach guidelines)

pH 8.5 to 9.0

Specific Conductivity 2.5 to 11µS/cm

Cation Conductivity <0.3µS/cmCation Conductivity <0.3µS/cm

Silica, max 20ppb

Sodium, max 20ppb

Dissolved oxygen, max 30ppb

SWAS Panel & Components

Sample Cooler

• Selection based on Application• Design Temp : 1250°C & Pressure

400Bar• Design outlet temperature 5°C

above cooling water temperature.• Sample cooler coils of Inconel 600

/ Stainless steel material./ Stainless steel material.• Truly Counter-flow design• Designed as per International

standards ASTM, ASME, • On-Line shell cleaning• Built-In safety Valve for CW line• 3 stage cooling in one Shell design• Removable coil & Shell

High Pressure Reducer

(Rod-in-Tube type)

• Rod-In-Tube Design• No filters required• Designed for High Pr. Up to 400

Bar• Outlet pressure 1 to 30 Kg/cm2

Adj.Adj.• Design Temperature : 350°C• Designed in accordance with

ASME-PTC 19.11 recommendations

• ON-LINE Cleaning (In-Situ) by retracting the rods without disconnecting the sample line

• Built-In Safety Valve

High Temperature Sample

Shut-off valve• Automatic Reset • Wide choice of operating temp up to

100°C• Body temp rated to 300°C• No operator Hazard, Functions

accurately even it is fully immersed accurately even it is fully immersed in WATER

• NO Power / Air Supply Reqd. (No wiring in wet panel)

• Rugged & Compact Design • Ram-type plug design provides tight

seal upon shutoff

Cation column in Wet panel

• Cation column are filled with Resin charged with H+ ions.

• Cation conductivity measurement eliminates masking effect of known/ desired chemicalschemicals

• Specific conductivity is always more than Cation conductivity in Boiler water / steam/ Turbine condensate.

Back Pressure Regulator

• To get uninterrupted, regulated flow at constant pressure

• Used for back pressure control in grab sample lines.

• Design Pressure : 250 Bar , Temp 80°C

• Regulated outlet pressure • Regulated outlet pressure irrespective of upstream fluctuations, and to get same flow output even at low pressures.

• Built-In Safety valve• PTFE lined stainless steel

diaphragm

Chillers & Cooling water Systems

• Required in areas where cooling water temperatures are high. (> 35 ˚C)

• Standby Compressor & Pumps

• Sample coils of Stainless • Sample coils of Stainless steel/ Inconel 600

• Capacity of compressor decided by requirements.

• Hermetically sealed Compressor.

• Environment friendly refrigerant

COMMON FAILURES IN SWAS PANELS PANELS

Cooler coil choked by poor

water quality

Cooler coil corroded due to

chloride

Open junction box in wet panel

Mild steel brackets in

wet panels

WELL DESIGNED SWAS PANELS

Walk-in Wet panel

Walk-in wet panel

SWAS wet panel for sugar plant -

Front view

SWAS wet panel for sugar plant -

Rear view

SWAS Dry Panel

Silica Analyser I

ASME PTC - 19.11-2008

The ASME PTC-19.11-2008 lists the overallrequirement for methods to condition Steam &Water samples in high pressure boilers to beanalyzed for pH, Conductivity, DO2, Silica,analyzed for pH, Conductivity, DO2, Silica,Hydrazine, etc. All good SWAS suppliers shouldfollow the guidelines both in letter and spirit toensure a trouble free installation.

JPMA recommendations for

SWAS panels

• Use rod in tube pressure reducer as per ASME.

• Avoid filters in high pressure lines.

• Blow down samples before every commissioningto avoid rust and dirt particles from enteringanalyzer sample paths.

• Use SS seamless tubing from first isolation valveto SWAS panel.

JPMA recommendations for

SWAS panels – contd.

• Use Inconel 600 for sample cooler tubing by default to avoid cooling water corrosion.

• Specify all SS fabrication for wet panels. • Specify all SS fabrication for wet panels.

• Install SWAS wet and dry panel in clean enclosed area with max 30 deg C ambient temp.

• Ensure adequate pressure in cooling water header.

JPMA recommendations for

SWAS panels – contd.

• Use mechanical thermal shutoff valves notsolenoid valves

• Choose a SWAS system supplier with a good• Choose a SWAS system supplier with a gooddesign team.

• Involve water chemists and instrumentmanagers of end user in SWAS specification.The site acceptance test should be witnessed bychemists , instrument managers and powerstation managers.

JPMA recommendations for

SWAS panels – contd.

• Check availability of analytical grade ofchemicals, silica free water and calibrationstandards for silica, sodium and dissolvedoxygen analyzers.oxygen analyzers.

• Ensure timely and regular maintenance andcalibration every season by original SWASsystem specialist.

Conclusions

• A SWAS system receives scant attention fromconsultant, OEM or end user as it constitutesless than 0.5% of the project cost.

• A good SWAS requires expertise in mechanical,process, instrumentation, civil engineering andwater chemistry.

• Even after installation SWAS requires constantattention , maintenance.

• In contrast costs resulting from a non workingSWAS are very high .

Conclusions contd.

• Power and production losses in a sugar complexdue to poor steam quality far outweigh theinstallation and maintenance cost of a SWASpackage.

• If it functions correctly, payback is less than one• If it functions correctly, payback is less than onemajor shutdown for 2 weeks.

• Repair charges for a turbine with silica depositsare more than one years maintenance chargesfor a SWAS.

Conclusions contd.

Operating a cogen system without a functionalSWAS is like driving in the dark withoutheadlights to warn you of what lies ahead.The risks of operating a plant “blind” are toogreat.

References

• 1.Cation Conductivity Monitoring: A reality check by David G Daniels – M&M Engineering Associates - POWER magazine May 2008.

• 2 Continuous Silica Monitoring in a Power Plant Application Note Hach company 2012.

• 3.Steam Generation in Power Plants –Application note – Power No 12 Hach Company www.hachultra.com

References contd.

• 4.ASME Power Test Code 19.11. (2008.) –Steam and Water Sampling Conditioning andAnalysis in the Power Cycle.

• 5.Indian Standards 10496 1983 (reaffirmed• 5.Indian Standards 10496 1983 (reaffirmed1994) Specification of feed water, boiler waterand condensate for high pressure boilers.

• 6. Seven Sins of Steam Sampling – ManuaelSigrist CTO, SWAN Systems AG published inPOWER plant chemistry 2010, 12(7).1

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