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IS 10021 (2000): Guidelines for De-icing System forHydraulic Installations [WRD 12: Hydraulic Gates andValves]

Indian Standard

GUIDELINES FOR DE-ICING SYSTEM FORHYDRAULIC INSTALLATIONS

(First Revision )

ICS 93.160

0 BIS2000

B U R E A U O F I N D I A N S T A N D A R D SMANAK BHAVAN,9 BAHADUR SHAH ZAFAR M-ARG

NEW DELHI 110002

July 2000 Price Group 4

Hydraulic Gates and Valves Sectional Committee, WRD 12

FOREWORD

This Indian Standard ( First Revision ) was adopted by the Bureau of Indian Standards, after the draft finalized bythe Hydraulic Gates and Valves Sectional Committee~had been approved by the Water Resources Division Council.

It is desirable to provide ice-prevention or de-icing systems for hydraulic structures located in areas where lowwinter temperatures cause heavy ice formation. Such system when operated prior to freezing of the surroundingwater. will prevent the formation of surface ice in critical areas and/or remove ice already formed, if operated afterfreezing. Ice prevention system may be used for various purposes, such as protecting the civil structures and gatesagainst ice pressure, keeping intake gatesintake stop logs, spillway gates, draft tube gates. etc. free of the iceformation in between stationary embedments and the moveable gate components which either remain in contact orhave very small clearance or preventing building up of ice against these structures and eliminating obstructionaryinfluence of ice on the operation of hydraulic control gates.

In cold climate, ice formation on crest and gates in open air should be prevented to ensure that they remainoperational as and when needed. If not done, ice will form in b[Treat quantities below leaky gates and the entireupstream face of exposed steel gates will be coated with the ice several centimetres thick. The ice which forms onthe face of the gates may be too heavy, for the hoists to lift. The ice will also adhere to the piers and sill. The icemust be kept clear of the upstream face of the gate, not only to permit operation but also to prevent thrust from theice sheet against the gates. This thrust has been known to damage the gates to a considerable extent.

Dependable operation ofcrest gates requires that lifting equipment can be made to function without fail.To achievethis the water in contact with gate on the upst.ream side, the guides, support roller tracks or sealing strips shouldnot be allowed to freeze.

The operation of mechanical/manual removal of large quantities of ice already formed in the gates is both slow andexpensive. Also, unsuccessful operation of frozen gates when required to pass sudden floods may endanger thesafety of structure. It will be therefore economical to make provisions in the gates to prevent ice formation.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value.observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance withIS 2 : 1960 ‘Rules for rounding off numerical valltes ( revised)‘. The number of significant places retained in therounded off value should be the same as that of the specified value in this standard.

1 SCOPE

‘This standard provides general guidance for thede-icing systems that can be employed to prevent iceformation in the hydromechanical installations ofhydraulic structures located in areas where low wintertemperatures cause heavy ice formation. These includedams, intake structures, trash racks,spillway gates,etc.

2 REFERENCE

The following Indian Standard contain provision whichthrough reference in this text constitute provisionsof this standard. At the time ofpublication the editionindicated was valid. All standards are subject to revisionand parties to agreements based on this standardare encouraged to investigate the possibility ofapplying the most recent editions of the standardindicated below :

IS No.

6206 : 1985

Title

Guide for selection, installationand maintenance of air compressorsupto IO bars ()~st revision )

3 ICE FORMATION

3.1 In reservoirs under very severe cold conditionsthree distinct forms of ice, namely, sheet ice, anchorice and frazil ice are likely to be formed.

3.2 Sheet Ice

This is the ice that gets formed in still water undernormal conditions and exists as a surface layer.

3.3 Anchor Ice

Anchor ice consists of small ice needles which getformed at the bottom of fairly quiet, shallow bodiesof open water or water covered by 3 thin transparentice sheet. it appears usually on cold, clear nights andbecomes loosened and floats away during the earlyhours of the day.

3.4 Frazil ke

Frazil ice consists of fine spicular ice crystals floatingin the water and formed by slight super cooling below0°C. This ice adheres to the surface ice and to theanchor ice. In engineering work fiazil ice is particularlyobjectionable as it adheres to the racks and to the

IS 10021 : 2000

Indian StandardGUIDELINES FOR DE-ICING SYSTEM FOR

HYDRAULIC INSTALLATIONS

( First Revision )gates. If due to exposure to the air, the gates or racksare slightly supercooled, the frazil ice freezes into onesolid mass.

4 SPECIAL ASPECTS

4.1 In very cold weatherwhere there is likelhood offormation of ice sheet over the reservoir, the additionalforce on account of ice thrust should also be consideredon the hydraulic structures under closed conditionof crest gates. The point of application being near tothe water surface level increases the overturning momentsubstantially due to high lever arm. The crest gates3s well as spillway structure if not designed for this.ice thrust, may get damaged. In addition, both veerticallift and radial gates on spillways may cause operationaldifficulties due to increased operation friction causedby the ice.

4.2 When gate in hydraulic structures should beconstantly available in operating condition in coldclimate, adoption of the type of gates/its sealingarrangements should be suitable to reduce leakage tothe minimum and the design and features of gate shouldbe such~that various methods of de-icing and ice removalare incorporated as per requirements of their sitespecific.

Gate embedded parts should be maintained ice free tominimize frictional forces and to prevent damage to.and gate bearing areas~and guide elements by rubbingagainst ice build up. Where heavy ice build-up isexpected next to the gate skinplate, heating shouldbe provided for the skinplate to maintain a fhin filmof water in between the skinplate and the ice sheet tokeep the gate operational. This is most likely on theprojects with relatively small reservoirs.

The sealing, bearing and guiding faces are generallyin contact with or having very small clearances fromthe gate components are the critical elements/locationsfor freezing with every type of gate. On vertical liftgates, these critical locations are the roller tracks,seal seats, guides which must be kept free of ice toensure good operation. Tight seals are importantbecause leakage becomes the starting point for freezingand may build up large masses of ice on the downstream side ofthe seals which may cause trouble evenif the seals and roller tracks and the guides are keptunfrozen.

I

IS 10021 : 2000

The gate should preferably have upstream skin plateand sealing. As far as ~possible the gate should belocated behind the crest wall/baffle wall. The top sealshould preferably be located below the expected icesheet thickness from full reservoir level.

4.3 In power plant intakes, located in cold climates, itis often necessary to adopt special precautions toprevent ice from interfering with the operation of plant.Frazil ice can travel significant distances beneath anice cover and be a potential hazard at trash racksprotecting water intakes against the passage of debris,trash, etc. The tendency for the frazil needles to adhereto the metal of the racks and to gradually build up anice coating, may initially result in increased head lossat the rack and may ultimately seriously impede thepassage of water through the rack and necessitateturbine shutdown.

It would be preferable to design trash racks to remainsubmerged at all times. It should be removable typeand if so required, upper section of racks can be removedduring winter flows, when floating debris are notexpected to react the trash rack location due to icecover.

4.4 Ice pressures are influenced by the nature ofreservoir shore. Steep rocky shores offer higherresistance to an expanding ice sheet and as a resultgenerally higher pressures develop than at flat andsandy shores. Field investigations may be necessaryto determine the ice pressures and advisability ofprotecting certain hydraulic structures against icepressures by de-icing systems.

4.5 To keep the hydraulic gate operable where iceformation is expected, the following may be givendue considrations:

4

b)

c)

4

e)

t)

Provide heating system for the gate embeddedparts and, if necessary for the gate skinplate.

Design the gate~and the hoist with capacitysufficient to overcome to a reasonable extent,the increased ice loading.

Make the sealing arrangement leak-proof asfar as possible.

Select de-icing arrangement/systems to sentsite conditions.

Provide adequate drainage to-prevent ice buildingup on the downstream face of the gate.

Do not open the gate at too small an opening.

5 DE-ICING SYSTEMS

5.1 The following de-icing systems can be provided

2

for ice prevention:

a) Air bubbler system, and

b) Heating system.

5.1.1 The crest type gates can also be provided withflaps at top, to be operated by hydraulic hoists or byother mechanical means. The operation of flap allowswater disturbance underneath the ice sheet therebyresulting in breaking the ice sheet. This system issuitable for de-icing of ice sheet of lower thickness(up to about 250 mm) and can be used independentlyor in conjunction with heating arrangement in theembedments/gates.

5.2 Air Bubbler System

5.2.1 This system comprises essentially of aircompressors to supply compressed air at suitablepressures to a main header(s) which in turn feedscontrol headers and then the distribution piping carryingnozzles at strategic locations, opening into the reservoir.

5.2.2 In a reservoir that is frozen, the temperatureof water increases with depth below the surface of ice,varying from 0°C adjacent tothe ice to approximately3.9”C the temperature at which water has its maximumdensity. In the compressed air bubbler system, air isforced through nozzles into the reservoir at a depthof not less than 3 m, adjacent to the structure to beprotected. The compressed air breaks into small bubblesand mixes with surrounding comparatively warm water.The stirring and mixing action ofthe released air inducesa strong upward current ofrelatively warm water whicheither melts the ice already formed or prevents itsformation.

5.2.3 This system is less common than the heatingsystem because it is relatively slow and less efficient.Bubbler system installation are generally provided atintake trash rack location or where the reservoirs arelarge and the gates not operated in winter. Moreoverthis system is less effective in gate grooves whereseals and trash racks are like!y to freeze. The bubblersystem should be continuously run during winter.This could prove too expensive depending on durationof winter usage.

5.2.4 Discharging air vertically down from the orificeresults in a superior flow pattern. A discharge of0.05 cu m of free air per minute is sufficient to inducea~strong upward current. Circulation is effective foran area varying from 5 to 6 m in diameter around theorifice. This influences the spacing of air nozzles toprovide the required coverage for the bubbler system.

For the purpose of spacing nozzles, circulation canbe assumed effective in an area of 4 m diameter aroundthe orifice.

5.2.5 Care should be taken not to thaw the ice awayfrom the projecting nose of the pier, which shouldtake the ice thrust. Conditions can be improved inthis respect-if the piers at the gates extend considerablyupstream so that the ice tends to span horizontallyfrom pier to pier, insteadflf exerting pressure on thegate.

5.2.6 Compressors

5.2.6.1 Air cooled compressors pf the reciprocatingpiston type or rotary type according to IS 6206 maybe used to supply compressed air. Up to dischargepressure 0.14 N/mm2 gauge single stage air cooled.rotary compressors, which ensure smooth vibrationless and continuous air delivery are preferred. Thecompressor eqlaipment should include an air filter.intake silencer, automatic unloader, checkvalve, pressuregauge and an oil separator. An air receiver should beused when the volume of air header is less than thatrequired to hold the total discharge of compressoroperating for one minute, with initial and final dischargepressures at atmospheric pressure and the normaloperating pressure respectively. Air receiver shouldbe equipped with a drain cock and a safety valve.

5.2.6.2 Compressors should be of the constant runningtype supplying its full capacity to the nozzles,automatically unloading the full capacity of thecompressor whenever a predetermined pressure isreached and automatically bleeding air offthe cylinderswhenever the machine is stopped. Capacity ofcompressors should depend on the operating head

IS 10021 : 2000

at nozzles plus all pipe losses.

5.2.6.3 The delivery of the compressor should becalculated on the maximum number of nozzles in useat one time. Maximum delivery should be 0.05 cu mper nozzle multiplied by the maximum number ofoperating nozzles and divided %y the volumetricefficiency of the compressor at maximum operatingpressure. .

5.2.6.4 Maximum gauge pressure should be 5 percentor IO percent more than the sum of maximum reservoirhead on the air nozzles, the differntial pressure acrossthe nozzle and the pressure loss in the piping system.

5.2.6.5 It is desirable to install compressors in pairs,with electrical controls for alternate operation of about8 h each. Fig. 1 shows typical air compressor andpiping assembly.

5.2.7 Layout of Piping

53.7.1 Each structure to be equipped with de-icingsystem should be carefully considered to ascertainthe location of features requiring protection againstice formation. In dams where fluctuation of reservoirlevels is anticipated during the winter months, two ormore sets of distribution pipes may be installed atdifferent levels to serve for the fluctuating water surface.

5.2.8 Placement of Nozzles

5.2.8.1 Compressed air nozzles should be placed atelevations that will permit operation at a minimum

AIR COMPRESSOR UNITSA,

L$ OF MAIN HEADER

.,

FIG. I AIR BUBBLER SYSTEM AIR-COMPRESSOR INSTALLATION

3

IS 10021 : 2000

submergence of 3 m and a maximum that will permitthe vertical flowing mixture of air bubbles and waterto protect the structure above. The space betweennozzles should not exceed 3 m which providesapproximately 4 m diameter ice free area around nozzles.Each set of operating nozzles should be at the sameelevation to ensure approximately equal dischargesfrom each nozzle. The compressed air nozzles shall beprovided with non-return valves to prevent back flowof water.

5.2.8.2 Fig. 2 shows typical arrangement of air nozzlesfor a trash rack structure.

5.2.8.3 For spillway gates the air nozzles should belocated not less than 2 m upstream from the face ofgates. A typical arrangement of air nozzles for a verticallift gate is shown in Fig. 3. Nozzles of short tube typewith a diameter of 3 mm and a length of IO mm havefavourable flow pattern and better non freezingcharacteristics.

5.2.9 Air Header

The main air header delivering air from the compressorto the distribution piping is usually placed in aninspection gallery in the dam or embedded in concrete.If embedded, the supply piping should be at leastI.5 m from the concrete face to prevent freezing.Galvanized steel pipes with galvanized iron or steelfittings are generally used for header.

5.2.10 Control Header and Distribution Piping

Control headers and distribution piping are made of

brass, copper or galvanized iron or anodizedaluminium or special PVC suitable for low temperature.Long radius bends, to facilitate cleaning whennecessary, should be provided. The control headerincludes an intake valve, a throttle valve to thedistribution pipe or pipes, a control valve for eachdistribution pipe and a drain valve. Normally the valvescontrolling the operating lines should remain fullyopen to allow the full compressor capacity to passthrough the operating nozzles. Fig. 4 shows a typicalcontrol header branching from an air header locatedin an inspection gallery, with a shut off valve and acontrol valve to control the air flow in embedded pipingleading to the air nozzles. Expansion joints should beprovided for pipes running across the contractionjoints of concrete dam or other concrete structures.These expansion joints absorb differential movementbetween adjoining concrete blocks.

5.2. I I lnstallution

Hydrostatic pressure should be maintained in theembedded piping during concreting and pressuregrouting. The piping should be inspected for leakswhile under pressure. Precautions should be taken toprevent damage to the copper tubing. Solder jointsconnecting the copper tubing and fittings should bemade in accordance with good established practice.

5.2.12 Operation

Since the bubbler system is normally designed to usethe entire capacity of the compressor, the operatingcontrol valves should normally remainfully open. A

r AIR HEADER

CLEARANCE LINE

DETAIL AT P

PLAN

FIG. 2 DISTRIBUTION PIPING IN TRASH-RACK STRUCTURE

4

IS 10021 : 2000

El r AIR COMPRESSOR UNIT

.I.I’.I F S L 1.2 .:;: :,

AIR PIPE HEADERTO OTHER GATE _/

S E C T I O N A A

T-7 ,- AIR COMPRESSOR T+1

UNITI

MPRESSED AIR

AIR PIPE HEADERTO OTHER GAT

PLAN

F I G. 3 AIR BUBBLER SYSTEM SP I L L W A Y

curve showing compressor discharge pressures forvarying reservoir levels should be prepared for operationon the basis of operating characteristics of the com-pressor. The proper use of control valves for boththe operating cycle and the shut down cycle shouldbe described in the operating instructions.

b)

c)

5.3 Heating System 5.3.2

and/or thermostat.

Steam -continuous heating is often desirable.and

Hot liquid or hot air-on acyclic basis controlledby timer and/or thermostat.

Heating by Electricity

5.3.1 Heating system is an effective means ofcombating 5.3.2.1 Heating by electricity can be accomplished

ice on the gates~because of fast action especially for by either the straight resistance or the eddy current

de-icing of seals and tracks of vertical lift gates, radial method. In recent developments electric resistance

gates and other operating points of gatesln this system heating has been used almost exclusively. It is the

heating is done by: simplest to apply and can be installed with the leasttrouble and with much less duct work than medium

a) Electricity -on a cyclic basis controlled by timer like stream and hot liquids.

5

IS 10021 : 2000

AIR HEADER

--IA -

I - - -. --_-ye-.----_-.

SHUT-OFF VA WESFOR DISTRIBUTION

THROTTLE

V-TYPESTRAINER

A-

F I G. 4 A IR B U B B L E R S Y S T E M A I R- CO N TROL HEADER

Electrical induction heating utilizes the heat generatedby currents induced in a metal part by the process ofinduction.

5.3.2.2 In this method space heaters are provided ina housing in the concrete near the gate seals. Theheating units should be of the tubular type consistingof heltcaly formed coil of crome nickel resistance wiresurrounded by refractory insulating material encasedin a seamless tubes of corrosion resistant and non-oxidizing metal. On account of great masses of waterand metal present the heating element should be ofample size.

5.33.3 To protect the concrete from very hightemperatures resulting in cracking of concrete on coolingand to keep its temperature within the safe maximumtemperature of 65°C thermostats are used whichdisconnect the transformers aUEOIIIaEiCdly when thetemperature is exceeded. The thermostats operate thebreakers connected to high tension side of eachtransformer. Circuit breakers are designed for manualoperation and it is possible to heat the plate on oneside ofpier w=ithout heating the other side.The possibletemperature differential due to this condition may createspecial problems in the design of piers and it may

become necessary to add extra reinforcing steel.

5.3.2.4 Suitable insulating material, like asbestos.should be provided in the block out behind the housingof the heating element to protect the concrete surfacefrom cracking and deterioration.

5.3.3 Heating by Steam

5.3.3.1 In this method steam pipes are embedded inthe concrete, housed in steam cells near the gate seals.The steam should necessarily be supplied continuouslyduring cold~climate, because if the steam coils areallowed to cool, condensation may freeze them solidwhen steam is first turned on.

5.3.3.2 The usual method is to supply steam throughwater boiler which could be either the coal or oil firedtype or the electrode type. Where the gates are inremote locations or there is likelihood of interruptionin power supply it would be desirable not to dependon electricity for the boilers but to have sufficientsupply of coal or oil for use during the winter months.The boilers should have to be able to supply steam atadequate pressure so that the steam can travel in the 1coils to the bottom most point and return to thecondensation tank.

5.3.3.3 To protect the concrete from very hightemperatures, thermostats are used to operate solenoidvalves on the supply line.

5.3.3.4 A typical arrangement of steam heating for avertical lift spillway gate is shown in Fig. 5.

5.3.4 Heating by Hot Liquid or Hot Air

5.3.4.1 In this method a liquid having a lowfreezing point is heated by electricity and circulatedthrough pipes embedded in concrete adjacent to the

IS 10021 : 2000

areas to be heated. By controlling the speed ofcirculation,temperature of the liquid should normallybe maintained between 40°C and 65’C.

6 PERIODIC OPERATION OF GATES

In some hydraulic installations, if it has not been possibleto make provision for any of the de-icing systemsmentioned earlier, it may be possible to break up anice formation by periodic operation of gates/regularcleaning of trash-racks during periods of severe frost.This may ensure satisfactory operation of gateswhenrequired.

HEATING MEDIA

WELD WATER-TIGHT

P L A N

FIG. 5 HEATING SYSTEM BY HOT LIQUID/AIR OR STEAM

7

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