System Maintenance of the Boiler

7/30/2019 System Maintenance of the Boiler

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4.1 System maintenance of the boilera) Daily maintenanceBlowingProceed to the tube bungle blowing with regularity, always

starting from the first blower following the gas way andafterwards moving to the others.Before the blowing, increase the air capacity and keep it forthe whole operation period.For a good boiler efficiency carry out a daily blowing,following the blowers manufacturer’s instructions.A gradual increase of the gas temperatures to the stack andof their pressure (measured through the different banks)indicate the necessity of blowing, after this, the functioningvalues will return normal.

Boiler blow-down The boiler must be purged nearly once a day in order torestrict the quantity of solids dissolved in the water boilerand to remove the mud deposits.When the boiler is working, discharge, preferably at low load;opening the appropriate valves under the inferior drum.

The drain valves of frontal and rear cuts-off must be neveropened when the boiler is working because the waterfeeding to the tubes may miss with their overheating and

possible damage.When it is installed, the micrometric valve for continuousdrain can be calibrated in order to obtain the requestedwater values tin the boiler.Water analysisFeed and boiler water must be used daily in order to checkthat the different parameters are according to valuesdescribed by manufacturer. (Tab. No. 7 and No. 8).B0 Overtime maintenanceExternal cleaning

The external cleaning of the pressure parts must be carriedout at intervals, in occasion of repairs during the workingperiods of during the normal visible checks.

The manual cleaning of the surfaces with scratchbrushes isacceptable, but the most efficient cleaning method for the



boiler, the heaters and the economizers is the cleaning withwater.With this method, using hot water, many soluble saltscontained in the deposits, are dissolved and are free, and

therefore are easily removable, the unsoluble deposits suchas carbon and ashes. The cleaning water must be available at a temperature of about 70 OC. and it must be discharged through theconnections.

The cleaning of the different parts must always begin fromthe top.After having removed all the deposits, a final cleaning mustbe carried out in order to eliminate all the acid solutionsfrom the washed surfaces.

Such acid deposits must be eliminated from the tubes endsand from the economizer and heater openings (wheninstalled).Internal cleaning

This maintenance has been already described in troubleshooking chapter.Boiler conservationShort stopWhen the boiler must not work for short periods,

precautions, must be taken in order to protect them againstcorrosions.In this case the boiler and the superheater must becompletely filled with hot degassed water in good alkalinityconditions (200 p.p.m. of hydrazine ph 10).All the drain and vent valves must be kept closed and a dailycheck must be carried out to assure that the boiler iscompletely full and that the alkalinity is kept.Long stopIf the boiler must not work for a long time (superior to fourmonths) have two conservation systems.1) Empty it completely and keep it dry both inside andoutside absorbing the moisture from limes boxes situated inthe furnace and in the drums.



Measures must be taken, in order to close also the openingsof the parts that join the boiler with the atmosphere (faninlet, flue).Each month check and change the lime.

2) Empty completely and dry the boiler.Close perfectly the valves on the pressure part.Open partially the vent valves of the drum and the steamoutlet.Connected the boiler to a bottle with pressure reduced theboiler and pressurized at 0.3 – 0.5 bar.When the nitrogen filled completely the boiler, closed thevent valves and keep this condition during the conservationtime.3.3.1 – Tubes rupture

Recommended procedure to follow in case of tube bursta) Find the fuel to burners.b) Increase the air fan capacity.c) Assure that the feeding is made in order to maintain asufficient water level in the boiler fan almost ten minutes toavoid overheating of the undamaged parts.d) Remove the plugs to gas side drains regarding thecombustion chamber and the bundle so that the water drainsoutside.

e) Close the steam valves.f) Open the safety valves by using the appropriate manualdevice.General description for temporary repairIn case of boiler pipe bursts, these can be pluged temporaryin order to continue functioning.

The faulty tubes will be replaced when it is necessary.As the pluging of a boiler tubes causes the elimination of water circulation and therefore a high overheating of thematerial.Particular cares can be used in case of repair of tubes, whichform the furnace.

The procedures, to be followed for the temporary repairs of boiler tubes, are describes on dwg. TAB 122 and consist of the following methods.a) Tubes of tube bundle



- Find out the faulty tube.- Introduce the proper tool from the inside of the drums tocarry out the manual circumferential cutting of the tube (thecutting must be carried out at about 25-40 far from the

external of the drum).- Carry out a longitudinal cutting with a thickness of the tuberemained in the drum. Be careful of not nicking the holesurface of the drum.- Hammer lightly the tube crop end until it is removed fromits place.- Check the hole in the drum; it must be cleaned and have afree seal surface. It must have no longitudinal scorings.- Eliminate trimmings at the corners, if there are any.- Introduce the plug external diameter 51 mm. – sp. 4 mm.

from the inside of the drum and expand slowly with theappropriate expander.- Avoid heavy lubrification during the expanding and cleanproperly after operation.It is better that the tube is under expanded rather than overexpanded.In the first case, a tube, which has losses during thehydraulic test, can be expanded again until elimination of the losses; in the second case, an overexpanded tube, with

losses during the test, can also have the necessity of beingchanged.b) Tubes of the combustion chamberfor the application of plugs on faulty tubes, which form thefloor, the lateral wall and the roof of furnace, is the samealready described for the tubes of the tube bundle.Afterwards the tubes will be protected at the inside of thefurnace with the system described on dwg. TAB 122.Such system consists of the application of refractorymaterial as protection of the pluged tubes, to avoid metalovvertemperatures and coming out of combustion gases.

The procedure is the following:- Remove the tubes part towards the furnace using a cuttingtorch.



During this operation, pay attention to not nicking theadjacent tubes and not remove the external seal welding of the combustion gases.- Weld inside the cut tubes some flat bars 30 x 4 in alloy

steel 2% Cr 1% Mo, which are cut at an end bent at V, sothat it is better to anchor the following casting of refractorymaterial, after the assembly of the net described afterwards.- The flat bars must be welded at a longitudinal pitch of about 200 mm. on the superior part forming the roof, of about 375 mm. on the vertical part forming the furnace walland can be omitted on the low part which forms the floor.- Among the welded flat bars must be inserted some platestrips in carbon steel – thickness mm. 3 to cover theopenings in the tubes obtained before with the cut at the

torch.- The height of the strips depends on the welding pitch of theanchorage flat bars carry out the welding pints for the stripsfixing.- Cover the part to protect with the metallic net, wire diam. 2mm.., mesh about 30 x 30 in carbon steel.

The net must be placed at about 40 mm. from the platestrips and must be stop-welded at the flat bars 30 x 4 whoseends can be now extended at y.

- Prepare a moisture of refractory grit at 42-44% of Al203and spindle cement 600, these in proportion 25-30% inrespect of the grit.- Cover the part of protect with a thickness of 200 mm.connected laterally till the two water tubes for each of twosides are covered.c- Tubes of the frontal and rear walls (Tab. N. 4)the procedure to be followed is indicated on dwg. TAB 122and is similar to the one already described for the tubes of furnace, except the part regarding the end connections forwhich it must be carried out as follows:- carry out the cut at the tubes torch on the side towards thefurnace.- check that the slot surfaces for plugs diam. 43 – thk. 4 aresmooth and without trimmings.



Remove all the metallic flakes or deposits, clean and expandwith the procedure already described in the followingparagraph.Protect the tubes with refractory material as for the former

tubes of the furnace. (Tab. N. 5)Replacement of tubes of the lateral walls, floor, roof,frontal, and rear furnace (Tab. N. 5)

The following method is valid both for the faulty tubesreplacement and for the repaired tubes in accordance withthe indications of dwg. TAB 122.In this last case, the used materials for the momentaryrepair must be obviously disassembled.- Carry out the first cut at the torch on the whole tube lengthand afterwards a second cut from the apposite part.

- Repeat these operations on the other side of the tube inorder to detach completely the tube to replace from the partin efficient pressure.- During these operations, it must be used the maximumcare not to ruin the adjacent tubes.- Eliminate remanents on the tubes also due to the cut withtorch, using a disk grinding wheel. Also for this workattention must be payed not to nich the tubes thickness.- Remove from their places, the materials for the temporary

repairs.- Check that the slot holes in the drums are in goodconditions if not rectify them, clean them carefully.- Check the inside of new tubes in order to assure that theyare free, therefore assembly and expand them as describedbefore. Restore the seal wilding of seal gas side welingcontinuously and using normal electrodes, on the same sideof the adjacent tubes.

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System Maintenance of the Boiler