MAC Boiler Manual (Extract)

7/26/2019 MAC Boiler Manual (Extract)

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MHI-MME Proprietary Information

2. Outline of Marine Boiler & Accessories

2.1 Boiler

This installation consists of two drum water tube MITSUBISHI MAC-**BF type marine boiler with oil

and gas combination burners located in the furnace roof. The unit is composed of a steam drum and

a water drum connected by a bank of inclined generating tubes. Other water side components

include : front screen tubes, side and roof water wall, front and rear water wall tubes, down-comers,

roof and bottom front wall headers, and roof and bottom rear wall headers. Each tube in the furnace

floor, side & roof, front and rear wall are jointed to the adjacent tube by welding. In this welded wall

construction, the tubes forms a gas-tight envelop three side of the furnace. Since the combination

burners are located in the furnace roof, the gas flow from the furnace is evenly distributed across thefront bank and generating banks, then, discharged from the uptake of boiler.

Fig 2-1 Construction of Marine Boiler


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2.2 Drum Internals

Steam drum internals consists of surface blow line, internal feed pipe, chemical feed line, baffles and

dry box. Steam generated in the boiler tubes enters the steam drum, where it is forced to pass

through a baffle located at the normal water level before entering the upper part of the steam drum.

Before leaving the boiler through the outlet nozzle, the steam must pass through the dry box located

at the top of the drum. Manholes fitted with hinged manhole covers are provided in the front head of

the steam drum and water drum. The hinges allow the manhole covers to swing into the drum clear of

the manhole.

2.3 Furnace

Water cooled walls are provided by lining the furnace side, floor and roof with a single row of 88.9 mm

tubes, and front and rear with a single row of 76.2 mm tubes. External down comers provide ample

circulation to water drum. The water cooled floor consists of 88.9 mm tubes traversing the furnace

floor from the water drum, then bending to form the furnace side and roof, which terminates in the

steam drum. Furnace front and rear wall tubes arranged from the lower to the upper water wall

headers cover front and rear furnace walls. Upper front and rear water wall headers are connected to

the steam drum. Because water wall tubes are jointed to their adjacent tubes in a welded wall

construction, they form a gas tight envelops lining the furnace.

Where openings are required for burners, access doors and soot blowers, they have been formed by

bending tubes back and to the side to form the opening and then back to their original plane to

continue the welded wall construction. The furnace water wall tubes including reheat furnace are

backed up by insulation buck-stays and a corrugated casing.

2.4 Saddles

Saddles are provided under the water drum and the front & rear water wall headers to support the

weight of the boiler. Rear saddle under the water drum is fixed and the front saddle has slotted bolt

holes, grooves and grease fittings to allow easy movement and lubrication. Grease fittings are

provided on both front and rear saddle of water wall header. The grooved saddles are free to slide to

allow for expansion of the boiler as it is warmed up. The sliding feet should be inspected and cleaned

as frequently as possible and should be greased at least each 600 boiler steaming hours. This

procedure is extremely important and should be followed without failure. There are cases on record

where pressure parts have failed because the sliding saddles and frozen in place, preventing

movement required during normal expansion.


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2.5 Economizer

An extended surface type economizer is placed above the boiler tube bank. The economizer is made

up of closely spaced continuous loop elements, which is welded to the terminal headers at both ends.

Each element shall be of 38.1 mm tubes straight carbon steel tubes with spiral steel fin, connected by

U-bends forming integral loop. All elements are supported at the front and rear side by tube plates.

On the outside of the terminal headers, handholes with covers are provided. Insulated steel casings

are provided around the economizer and large removable panels are fitted on the front and rear side

for access and tube removal. Feedwater enters the inlet header at the top and flows through the

elements counter flowing to the gas leaving the boiler, to the lower header, thence to the boiler steam

drum.

2.6 Boiler Accessor ies

Boiler accessories are listed on this section later with the manufactures name and identifying data.

See instruction books of those accessories for detailed description.

2.6.1 Oil / Gas Combination Burner

The boiler is equipped with two (2) sets of fuel oil and gas combination burners on the roof wall of the

furnace. The fuel combination burner is of steam assisted pressure jet type, consisting of atomizer

gun, forced draft air register with fuel shut off valve. The fuel is distributed to each burner from a

burner manifold by branch connection pipe. The operation of start or stop of the burners is

automatically operated by the automatic combustion control signal, and remotely operated by the

push button when necessary.

Note; Oil / Gas combination burners are provided by Hamworhy Combustion, hence

instruction details to check their instruction manuals.

2.6.2 Automatic Combust ion Control

The control system is capable of controlling each boiler separately or all boilers together. The control

system is also capable of burning fuel oil only, fuel oil / gas together or fuel gas only at normal

operating condition. The boiler is arranged for all equal load sharing and each is capable of operating

in a single boiler mode. The restart of one boiler and transfer to gas firing does not affect the

continued operation of the other running boiler. The system control total fuel quantity and combustion

air quantity according to steam demand, and to maintain steam pressure constantly at main steam

outlet. The total fuel quantity for each boiler is the sum of fuel oil flow and gas flow to each boiler. The

calibration of these signals is such that they are of equivalent calorific value. Combustion air for

burner is supplied by forced draft fan. And combustion air quantity is controlled in accordance with

total fuel quantity by the forced draft fan inlet vanes.

Note; Automatic combustion contro l system is provided by Hamworhy Combustion, hence



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2.6.3 Feed Water Regulator

The boiler water level control system shall be two (2) element type sensing steam flow and drum level.

The feed water flow is controlled automatically by the regulating valve in accordance with variation of

water level to maintain the water level constant. And steam flow is used as feed forward signal. The

water flow can be also adjusted manually and independently. In case of control air supply failure, the

regulating valve is locked.

Note; Feed water control system is provided by Hamworhy Combustion, hence instruction

details to check their instruction manuals.

2.6.4 Burner Management System

The BMS is a system operated by manual local / remote control of FO and GAS fired burners or by

automatic operation linked with ACC.

Should any abnormality occur the BMS system will, after indicating an alarm, trip the fuel supply to

the boiler which is in an abnormal condition.

Note; Burner management system is provided by Hamworhy Combustion, hence instruction


2.6.5 Soot Blower

The boiler is equipped with soot blower system of steam nozzle tube type to clean the external

surface of tubes. The tunmber of soot blowers are as follows:

Position No. Type

Boiler bank tube Two (2) Stationary rotary

Economizer Six (6) Stationary rotary

Soot blower of stationary rotary is driven by electric motor. All soot blowers are automatically and

sequentially operated from the soot blower operating panel at control room.

Note; Soot blower contro l system is provided by Hamworhy Combust ion, hence instruc tion


2.7 Manufacturer List for Boi ler Accessories

Equipment Manufacturer

(1) Oil / Gas Combination Burner

Boiler & Soot blower controls

Boiler instruments

Hamworthy Combustion Engineering Limited,

(2) Safety Valve Fukui Seisakusho Co., Ltd.

(3) Soot Blower Clyde Bergemann Ltd.

(4) Water Level Gauge Nihon Keiki Co., Ltd.

(5) Valves mounted on the boiler Mitsumoto Valve Mfg Co., Ltd.

(6) Feed water control valve Nippon Fisher Co., Ltd.

(7) Chemical Dosing Equipment Taiwan Nikkiso Co., Ltd.


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2.8 Design Data

PRESSURES (bar)

Design 18

Operating (Main Steam Outlet) 16

Hydrostatic Test (Maximum) 27

Safety Valve Settings:

Steam Drum 18

Economizer 22.5

TEMPERATURE (degree C)

Steam SaturatedFeed Water 135

EVAPORATION (kg/h)

Maximum Capacity 80,000

FURNACE VOLUME (m3)

Furnace 84.7

HEATING SURFACE (m2)

Boiler 955

Economizer 1542

WEIGHT (kg)

Total Cold Water to Fill Unit Completely 41,800

Cold Water to Fill Boiler to Normal Level 30,400

Cold Water to Fill Economizer 2,200

Boiler, Dry, Complete with Burners and Soot Blower 85,600

Economizer, Dry Complete with fittings 24,400

Boiler Water, Steaming Condition 26,100

Economizer Water, Operating Condition 2,200

Total One Boiler, Steaming Condition 111,700

Total One Economizer, Operating Condition 26,600


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2.9 Tube Data

Location (Material) Quantity / BLR Diameter

mm

Thickness

mm

Rear Bank Tubes 928 50.8 2.9 or 3.2

Roof, Side & Floor Water Wall Tubes 45 88.9 5.5

Front Water Wall Tubes 33 76.2 4.0

Rear Water Wall Tubes 33 76.2 4.0

Front Bank Tubes 45 88.9 5.5

Rear Bank Front Wall Tubes 16 76.2 4.5

Rear Bank Rear Wall Tubes 16 76.2 4.5

Gas Outlet Water Wall Tubes 32 88.9 5.5


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2.10 Performance Data and Curve

1. AUXILIARY BOILER PERFORMANCE DATA & CURVE

MAC-80BF(100B) BOILER EXPECTED PERFORMANCE DATA FOR GAS FIRING

Natural Gas Case

LOAD % 10 25 50 75 100

EVAPORATION kg/h 8,000 20,000 40,000 60,000 80,000

DRUM PRESSURE bar 16.0 16.0 16.0 16.0 16.0

FEED WATER TEMPERATURE deg.C 135 135 135 135 135

SATURATED STEAM TEMPERATURE deg.C 204.3 204.3 204.3 204.3 204.3

BOILER EFFICIENCY (LHV BASE) % 87.8 89.9 90.6 90.4 90.0

HHV MJ/kg 53.85 53.85 53.85 53.85 53.85

LHV MJ/kg 48.76 48.76 48.76 48.76 48.76

FUEL CONSUMPTION kg/h 416 1,015 2,015 3,028 4,056

EXCESS AIR RATE % 25 16 9 8 7.5

O2RATE % 4.3 2.8 1.7 1.5 1.5

COMBUSTION AIR FLOW kg/h 8,930 20,050 37,430 55,770 74,570

kg/h 9,350 21,070 39,450 58,800 78,630

m3/h 11,250 26,610 52,310 77,980 107,180

AMBIENT AIR TEMPERATURE deg.C 25 25 25 25 25

deg.C 138 144 155 169 184

Note)

- Maximum flue gas temperature at boiler out let is abou t 450 degree-C.

FUEL GAS CHEMICAL COMPOSITION Nitrogen : 1.0800 Vol %

Methane : 96.7299 Vol %

Ethane : 0.9890 Vol %

Propane : 0.0000 Vol %

Butane : 0.0000 Vol %

Pentane or Heavier : 0.2701 Vol %

Water : 0.9380 Vol %

CALORIFIC VALUE

FLUE GAS FLOW

- Flue gas flow of vo lume base is actual cond ition volume flow at boiler outlet, not standard condition

volume flow.

- In case that ambient air temperature is 28 degree-C, boiler expected performance data is the same with

above figure.

FLUE GAS TEMPERATURE AT

ECONOMIZER OUTLET

1

1

1

2

2

4

4


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MAC-80BF(100B) BOILER EXPECTED PERFORMANCE DATA FOR MGO FIRING

LOAD % 10 25 50 75 100

EVAPORATION kg/h 8,000 20,000 40,000 60,000 80,000





HHV MJ/kg 46.01 46.01 46.01 46.01 46.01

LHV MJ/kg 43.12 43.12 43.12 43.12 43.12


EXCESS AIR RATE % 49 31 18 16 15

O2RATE % 6.9 5.0 3.2 2.8 2.7


kg/h 10,840 23,320 41,680 61,530 81,910

m3/h 12,690 28,870 54,700 80,310 107,390


deg.C 139 145 154 167 181

Note)

- Maximum flue gas temperature at bo iler outlet is abou t 450 degree-C.

FUEL OIL : MGO (ISO 8217 DMA grade)

CALORIFIC VALUE

FLUE GAS FLOW

- Flue gas flow of volume base is actual condition volume flow at boiler outlet, not standard condition

volume flow.


above figure.


ECONOMIZER OUTLET

2

4

4

4


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MAC-80BF(100B) BOILER EXPECTED PERFORMANCE DATA FOR Crude Oi l FIRING

LOAD % 10 25 50 75 100

EVAPORATION kg/h 8,000 20,000 40,000 60,000 80,000





CALORIFIC VALUE LHV MJ/kg 40.7 40.7 40.7 40.7 40.7


EXCESS AIR RATE % 49 31 18 16 15

O2RATE % 6.9 5.0 3.2 2.8 2.7


kg/h 10,790 23,200 41,490 61,260 81,540

m3/h 12,740 29,060 55,290 81,200 108,590


deg.C 139 145 154 167 181

Note)

- Maximum flue gas temperature is about 450 degree-C.

FUEL OIL : Crude Oil (LHV : 40.7 MJ/kg)

Methane : 0.177 mol %

Ethane : 0.017 mol %

HC Liquids : Balance

FLUE GAS FLOW

- Flue gas flow of volume base is actual condition volume flow at boiler out let, not standard condition

volume flow.


ECONOMIZER OUTLET


above figure.

3

4

4

4


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MAC-80BF(100B) BOILER EXPECTED PERFORMANCE CURVE

84.0

86.0

88.0

90.0

92.0

94.0

96.0

0 10 20 30 40 50 60 70 80 90 100

Efficiency[%]

Boiler Load [%]

MGO

Natural Gas

Crude Oil

0

1,000

2,000

3,000

4,000

5,000

6,000

0 10 20 30 40 50 60 70 80 90 100

FuelCon

sumption

[kg/h]

Boiler Load [%]

MGO Natural Gas Crude Oil

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 10 20 30 40 50 60 70 80 90 100

O2Rate[%]

Boil er Load [%]

MGO

Natural Gas

Crude Oil

1

34


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3.7.6 Limi ts of Chemical Concentration

Feed Water Boiler Water

pH at 25 deg.C 8.5 9.7 10.5 11.5

Hardness (as CaCO3) mg/L Not detected -

Dissolved Oxygen mg/L 0.5 or less -

Oil mg/LTo be kept low as far

as practicable-

Phosphate Ion (PO43-

) ppm - 10 30

Silica (SiO2) mg/L - 50 or less

Chloride Ion (Cl-) mg/L - 150 or less

Dissolved Solid mg/L - -

Note 1 : Feed water in this table means the mixture of condensate and distilled water to supply into the boiler.

Note 2 : Estimate the pH value from alkalinity tends to give pH readings varying with silica, Ca, Mg, and other

salt contents of boiler water and hence is not necessarily deemed appropriate : resort to this method

only as a means to obtain a rough guide (alkalinity serves merely as an marine means in determining

the pH level). Also, be sure to control pH to the target value while, on the other hand, keeping

alkalinity at the minimum necessary level. Limiting the P alkalinity to within a certain range would

make it possible to inhibit the alkali corrosion even if boiler water concentration should take place on

the heating surface, etc.


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3.7.7 Chemicals and Quantity for Boi ler Water & Feed Water

(1) Chemicals to be used

For adjusting pH value and PO43-

: NaOHand Na3PO412H2O

For deoxidization and rising pH value : Hydrazine hydrate

(2) Dosage

A. Initial dosage

Pressure[P] (MPa)

ChemicalsP1 1


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3.7.8 Fuel Trip and Alarm Point of Water Level

Note :Remote water level indication is supplied by Hamworthy Combustion

375

200

72.

5

375

240

57.

5

200


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3.7.9 Relation between Drum Water Level and Water Content


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3.7.10 Boiler Pressure Raising Curve

0

0.5

1

1.5

2

0 60 120 180

Drum

Pressure(MPa)

Operating Time After Light Up (minute)

Boiler Pressure Raising Curve


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4. Outline of Maintenance

4-1



4.1 Feed Water & Boiler Water Treatment

Feed water and boiler water shall be analyzed at least once a day. Amount of chemicals to be

added and amount of boiler water to be blow down shall be controlled referring to the results of

the analysis so as to maintain each chemical content of the water within the prescribed limit.

Operators are required to have correct understanding about the action and effect of each

chemical and calculation method of required quantity of it.

Recommended chemicals are as follows

For adjusting pH value and PO43-

: NaOHand Na3PO412H2O

For deoxidization and rising pH value : Hydrazine hydrate

Keep quality of bo iler water and feed water correctly.

4.2 Maintenance during Shutdown

There are two ways of laying up the boiler, dry and wet. Either way may be adopted as the case

may be. When the boiler is laid-up wet, care should be taken to the concentration of chemicals

in the boiler water, and when the boiler is laid-up dry, care should be taken to the effectiveness

of the drying agent.

4.3 Hydrostatic Test

There are two kind of hydrostatic test, one for checking water-tightness of pressure parts and

the other for checking strength of the same. Test pressure should be determined to suit the

case.


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4.4 Boil ing Out

Boiling out is intended to cleanse the boiler internal surface of oil and grease. The boiler is filled

with high alkaline solution and is heated for a predetermined duration by means of steam or byburning oil whichever the occasion demands. Boiling out by burning oil is often made to serve

as burning and drying out refractory used in the boiler setting, too. Recommended duration of

boiling out for a new boiler is 23 days.

Boiling out chemicals is highly corrosive.

4.5 Water Washing

Hot water washing is intended to remove sludge sticking to the gas side of the boiler that

cannot be blown off by soot blowing. There are two ways for hot water washing, one by use of

soot blowers and the other by use of a temporary hand nozzle. Both ways have their own

merits, either way may be adopted as the case may be. Hot water washing is generally

required 68 hours. Hot water air heater shall be washed by use of water hose.

Recommended hot water temperature is about 80 degree C and pure water of 50 ton shall be

required.

4.6 Acid cleaning

Acid cleaning is intended to remove scales on the water side of the boiler. Inhibited hydrochloric

acid solution is generally used for this purpose. But it is important to consult with the

professional expert as to the details of cleaning job so as to take most suitable measures to the

actual case and to prevent damage that may result otherwise.

4.7 Refractory

As a refractory, castable type is applied. This refractory is often used for repairing work. When

the castable refractory is to be used on the pressure parts, it should be given necessary

clearances for thermal expansion. After repairing refractory work, never fail to dry it out by

firing.


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4.8 Boi ler Proper and Water Walls

Inspect both gas and water sides of the boiler whenever the opportunity is afforded and seewhether it is necessary or not to clean the gas side, to acid cleaning the water side or to replace

tubes. Results of these inspections should be referred to in the subsequent burner operation,

feed water control, etc.

4.9 Economizer

By-pass operation using Auxiliary Feed Water line can be applied when economizer tubes are

damaged. Faulty tubes shall be repair as earlier as possible.

Note; Economizer by-pass operation is not applied to this project as project requirement.

4.10 Boiler Drum Support Legs

The water drum support legs on the boiler rear side are the only fixed legs, and all the other

legs are of sliding type requiring the injection of grease once a year.

(Grease : Shell Alvania EP No.2, Mobilux EP No.2 or equivalent.).

4.11 Boiler Repair

The boiler repair work includes the tube plugging, header end plate renewal, removal of

manhole cover, tube renewal, expander renewal, packing renewal, etc. It is required that the

boiler operator be familiar with the working procedures therein involved.

4.12 Maintenance of Accessories

4.12.1 Burner

The burner tip is to be cleaned periodically and examined for disorder. The swirler is to be

maintained as clean as possible, and also the burner throat area is to be always kept in good

working order.


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4.12.2 Soot blower

The soot blower steam line drain discharge, smoothness of rotary motion, and adequacy of

lubrication are to be monitored. In the process of boiler open-up inspection, the element nozzle

is to be examined for disorder and also the element for bend.

The soot blower steam line drain discharge should be carried out

before operation o f soot blower.

To make sure no steam leakage from soot blower mounted inlet valveinto blowing element.

4.11.3 Automatic Combustion Control System and Automatic Feed

Water Regulator

By taking the control unit indicator reading, the control performance of each system is to be

monitored. The air supply line drain is to be blown out every one week. The moving parts of

every equipment are to be kept always clean or grease-up periodically for rust prevents

purpose as necessary

.

Note; Burner management system is provided by Hamworhy Combustion, hence


4.11.4 Water Level Gauge

The gauge glass is to be blown clear at least once a day to ascertainits responsiveness. The remote-reading level gauge reading is to be

compared with the gauge glass reading (once a day) to ascertain its

reliability.


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4.12 Check Point List

IMPORTANT

The followings are to be checked periodically to operate boiler safely.

Item Check Method Check Interval

Water GaugeCheck Water level response at opening or

shutting blow valve.1 / Day

Boiler, boiler casing,

ducts etc.

Check no harmful vibration at boiler, casing,

valves, ducts, piping, tubing, detecting lines or

pressure accessories related to the boiler.

1 / Day

Remote Water Level

Indicator

Compare the remote water level indicator with

transparent level indicator at 100 mm decreased

water level below normal. Manually operate FWR.

1 / 2 Weeks

Combustion condition

and Flame Detector

Check combustion condition. And its normal

condition to indicate burner flame failure to each

burner at only each burner firing.

1 / Day

Air Slide Operation of

Burner

Close or open the air slide manually at boiler side.1 / 2 Week

Water Level AlarmPoint

Check the water level alarm point, manually to

operate FWR at boiler lower load.1 / 3 Month

Fuel shut off valve for

safety system

Check operation of each fuel shut off valves such

as fuel oil shut off valve, fuel gas shut off valve1 / 6 Month

Leakage of Steam or

Water

Inspect boiler pressure parts, water level gauge,

flanges and valves.

Fuel gas line

expansion joint

Inspection leakage and inside condition.

(Confirm no sulfur corrosion in BOG piping

caused by combustion gas back flow.)

1 / 2 Year

Sliding surface of

boiler and economizer

feet and valve stem

Check the condition of sliding surface and to

make sure no harmful rust or scratch. Put make

up grease periodically.

1 / week

Casing / Insulation for

boiler, economizer

and duct

Check the condition of casings and to make sure

no harmful damages or no gaps between plates.

Note; Water ingress to protect by casings.

1 / week

Painting for boiler,

economizer and duct

Check the condition of painting and touch up if

required.1 / week


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4.18 Condi tion of the Emergency Fuel Oil and Gas Cut

Recommendation for customer only.

Boiler is shut down by the condition as follows.

Particular Set Point Location Remarks

Drum Level Low-Low -240 mm Local After 7 sec., off signal

Electric Source Failure - Local

Both B.M.S. Controller Abnormal - Local

Emergency Hand Trip Switch - ECR & Local

Forced Draft Fan Stop Over current Starter

All Burner Flame Failure Flame Out Local After 0 sec, off signal

Control Air Press. Low-Low 4 bar Local

Emergency fuel oil shut off valve is shut down by the condition as follows.


Fuel Oil Pressure Low-Low 1 bar Local

Fuel Oil Temp. Low-Low n/a n/a

Atom. Steam Press. Low-Low 3 bar Local

Fuel Oil Pump Stop No voltage Starter

Boiler Trip - Local

Emergench fuel gas cut valve is shut down by the condition as follows.


Fuel Gas Pressure High-High n/a Local

Fuel Gas Pressure Low-Low n/a Local

Master Gas Valve Trip - Local

Boiler Trip - Local

Emergency master gas valve is shut down by the condition as follows.


Emergency Hand Trip Switch - ECR & Local

Gas Leak Detection - Local

Cargo Tank Pressure Low-Low - Local

Fuel Gas Temp. Low-Low 5 deg.C Local

Both Gas Duct Exhaust Fan Stop - Local

Both Boiler Trip - Local

Both Boiler Gas Valve Trip - Local


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6. General Maintenance

6-9


5) Place test clamps (gags) on all safety valves. Safety valves should never be opened by

hydrostatic pressure.

6) The pressure gage used should be checked, before applying the maximum test pressure.

7) When filling the boiler open the vents on the boiler drum to bleed off all air, close the valve

when water runs out.

8) Before lowering the pressure, take up the slack on the nuts of the handhole and manhole

fittings, were new gaskets have been fitted. The nuts should be pulled just snug with the

wrenches supplied for the purpose. Do not use a pipe or other extension on the wrench handle.

9) When inspection is completed, open the vent valves and lower the pressure slowly by cracking

a drain valve. Use one of the bottom blow valve. Before starting to drain the boiler, be sure to

open the vent valves.

10) Remove the safety valve gags, replace the lifting levers and easing gear.

6.9 Boil ing Out

If the presence of oil is found on the waterside of the boiler, it must be removed by boiling out. This is

necessary after assembly of a new boiler, after completion of repairs requiring extensive replacement

of tubes, or if oil has entered the feed water from some other source. Boiling out is also a quick and

efficient method of removing various types of scale. The chemicals to be used and the strength of

solution required, depends on the character of the scale. Consult the boiler water chemist. Boiling out

to remove oil requires the use of a fairly strong caustic solution. One such solution is about 2 kg of

caustic soda and about 4 kg of hydrated trisodium phosphate, for each 1,000 kg of cold water

required to fill the boiler. This chemical solution is sufficient to remove ordinarily compounded

lubricating oils or the usual protective oil coating applied to tubes before shipment. Straight mineral

lubricating oils used for high temperature engines require stronger solutions. If such oil is present in

the boiler use about 2 kg trisodium phosphate and about 5.5~6.5 kg caustic soda per 1,000 kg of

water. In addition it is advisable to add detergent (wetting agent) amounting to about 0.5 % of the

boiler water. There are other chemical solutions which can be used. There are many satisfactory

compounds for boiling out, they are sold under various trade names by reputable firms. When such

compounds are used, follow the manufactures instructions.

6.9.1 Steaming Method

Boiling out may be accomplished by injecting steam through temporary lines into the bottom blow.

Temporary drip lines are connected to the boiler air vent and starting valve. The drip lines should be

open drains to portable tanks or drums, which are used for inspection and measuring tanks.

1) A chemical injector is used to inject the chemical solutions into the boiler, water wall as required.

The chemicals are dissolved in water and injected into the boiler, water wall, in proportion to the

weight of cold water required to fully fill each part. The water weights of each part are listed

under "2.11 Design Data".


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2) After injecting the dissolved chemicals, slowly start admitting steam, allowing the condensate to

fill the unit, until water overflows from the vents of the boiler.

3) Then throttle the vents and steam injection valves to maintain a pressure of about 0.4 MPa on

the unit, and to allow some overflow from vent. Regulate the vent valve so that the overflow is

roughly in proportion to the weight of water of each part of the unit.

4) The progress of boiling out can be determined by examination of samples from the drip lines.

Check the alkalinity of the samples, and inject additional chemical solution as needed, to

maintain a satisfactory strength of the solution. Continue boiling out until no trace of oil can be

found in the samples taken from the drip lines.

6.9.2 Firing Method

If steam and electric power are available and the auxiliaries are ready for service a boiler can be

boiled out using a light fire. When the firing method can be used, it is much simpler and does not

require temporary piping. The same chemical solution is used as described in the preceding method.

The quantity of solution to use should be figured for the weight of cold water required to fill the boiler

to normal steaming level. (See "2.11 Design Data".)

1) Make certain that no personnel are in the drum or in the furnace.

2) After filling some water, about half amount of chemicals shall be admitted into the water drum.

Manhole shall be closed and the boiler shall be filled the water again. Solid chemicals should

be dissolved with water before admitted.

3) When the boiler water has been filled in the steam drum to some degree, rest chemicals shallbe admitted into it through manhole.

4) When necessary amount of chemicals has been admitted into the drum, manhole shall be

closed and the boiler shall be filled up to the normal water level.

5) Using one burner, burner shall be fired at 0.3 MPa of oil pressure for about 5 minutes at rest

about 10 minutes interval. After repeated 2 hours, then burner shall be fired again for 10

minutes at rest 5 minutes interval. It is to avoid for burning of refractory and rapid thermal

expansion. The boiler shall be fired at a rate to start steaming in about 2 hours. MGO shall be

used with air atomizing. Valve operation during pressure raising, refer to 5.2 Starting a Boiler

from Dead Ship Conditions.

6) Boiler pressure shall be raised slowly to reach about 1.4 MPa after 4 hours of oil burning.

7) Boiler pressure shall be maintained at 1.4 MPa during the soda-boiling period.

8) When oil content of boiler water can not be measured, soda-boiling shall be continued for 8

hours. When oil content of boiler water can be measured, after holding the boiler for 3 hours at

soda-boiling pressure of 1.4 MPa, sample of boiler water shall be taken at every 1 hour to be

checked of its alkaline strength and oil content. If the oil content of the sample water has

become to show no more increase at each measurement, that is, when no further operation of

soda-boiling is thought necessary, soda-boiling can be terminated even before 8 hours have

passed.


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9) If the water level gauge is fouled with oil in soda-boiling operation, it shall be cleaned by

blowing steam by closing water-side root valve and opening drain valve of the gauge.

6.9.3 Wash and Inspect

1) After boiling out is completed, by either the steaming of firing method, blow down the boiler

through the water drum bottom blow off valve while the boiler is fairly warm. Discharge the

water overboard, to avoid damaging paint in the bilge by the strong caustic solution.

2) Open up the boiler and wash down with a high pressure water hose, playing the hose into all

tubes.

3) Carefully inspect the boiler, and if any trace of oil remains, repeat the boiling out process.

6.10 Water Washing Fireside

The heavy oil is the last extracted fuel oil in the refining process of crude oil, therefore includes the

ingredients causing slag on the gas side surface, and also is apt to includes the component of the sea

water due to marine transportation which promotes the slag accumulation in the boiler. Slag is a

mixture composed of sodium sulfate or a mixture of sodium sulfate and vanadium pentoxide, and

lesser amounts of the oxides of other impurities. When burners are kept in proper adjustment, the

atomizer kept clean and in good condition, and the soot blowers operated at correct intervals, slag

formation may be slowed down. However slag formation will eventually accumulate on the tubes and

should be removed before it has bridged over between tubes. Water washing schedule should be set

up to coincide with normal fireside cleaning. Operating practice will indicate at what intervals of

fireside cleanings water washing is necessary. Since slag is soluble in hot fresh water, hot fresh water

is sprayed on the slag encrusted tubes with a lance, using sufficient force to soften the slag and

knock it off the tubes. There are two methods in water washing. One is to use a hand nozzle and the

other is to utilize the soot blower in spraying hot water. The former permits concentrated washing of

important points so that effective washing can be done with relatively small quantity of water resulting

in less moisture of the boiler; but much time and labor is required. With the latter, washing can be

done easily in a short space of time but it requires relatively much water resulting in larger moisture of

the boiler. Water washing is usually carried out at a dock. A member of the crew can do it quite easily.

If preparation has been made in advance while the boiler is cooling, water washing will be done in 6

8 hours although it depends on the extent of dirtiness. The following is the order to processes of

water washing with a hand nozzle.

1) Prepare an apparatus to supply adequate quantity of hot water and a hose and nozzle for

spouting hot water.

2) Remove the casing access doors and dusting panels to facilitate the work.

3) Provide a means for immediate and constant draining of the waters and the removal of thesludge, resulting from washing down.

4) Water under 1.8 MPa and at a temperature of about. 6590degC should be sprayed on to the


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tubes, using an armored hose. Work from the top of the boiler down. In cases where slag

removal is extremely difficult, secure from washing, and allow the water to soak into the slag for

a period of 30 minutes to one hour. Then continue washing down the tubes.

5) Attention should be paid not to let washing water penetrate behind the bricks. It will be effective

to lay a sheet of canvas on the furnace floor. If small quantity of water is absorbed by bricks and

heat insulating materials, the bad effect will be removed by slowly drying soon after the finish or

washing.

6) It is desirable that the water washing is finished within 8 hours.

7) As soon as possible after washing is completed, light up the boiler, using one burner at a time.

The drying out operation should be done very slowly and should be continued until the boiler is

thoroughly dried out. The drying should be made at least for 12 hours.

Attention should be paid not to let washing water penetrate behind

the bricks.

6.11 Acid Cleaning

6.11.1 Introduction

Safe and efficient methods of cleaning boilers by acid washing have been developed to remove scale.This work should be done by contractors having experienced and competent personnel with proper

equipment. The following information is herewith presented for the general information of the operator.

This discussion will be limited to the cleaning of the boiler circuits. The following should be supplied:

1) An acid filling tank of sufficient capacity to hold the prescribed amount of acid and inhibitor.

2) One centrifugal acid filling and circulating pump with bronze impeller designed to deliver a

minimum of from 0.20.4 m3/min at 35 mTH or of such capacity as to fill the unit in not more

than 2 hours.

3) Suitable temporary piping and fittings to connect both the pump and tank to the boiler.

4) Cleaning chemicals.

A typical cleaning solution would contain 2834 % hydrochloric (muriatic) acid, an inhibitor and

water. The amount of acid used would be roughly 1020 % by volume of water necessary to fill

the component to be cleaned. See "Design Data. Selection of the concentration of acid used (1

6 % by weight for any one unit) depends upon the type and amount of scale or rust and other

impurities to be removed. Special attention must be given to ensure that the acid solution is not

enriched by ferric or cupric ion, which can be caused from the removed scale or deposits

containing a large portion of ferric or cupric oxide. This will impair the effect of the inhibitor. In

such a condition, keep the acid solution below the maximum allowable concentration of ferric or

cupric ion, by adding or renewing the reducing agent.


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6.11.2 Procedure

1) If more than a trace of oil is found in the boiler, it must first be boiled out with an alkaline

solution. A boiling out period of from 610 hours in adequate, when followed by acid cleaning.

2) Remove all tools, rags and other foreign material from the waterside of the boiler. Secure all

handhole plates, the manhole plates and valves, that will make the boiler watertight and

isolated from all boiler accessories except the water gauges.

3) Extension should be connected to the highest vents in the boiler, to ensure safe removal of

hydrogen gas, generated during the acid cleaning. Allow no welding during the acid cleaning

process.

4) Temporary piping should be connected from the filling tank to the filling pump suction, and from

the filling pump discharge to the lower water wall header drains. Piping should also be

connected from the most convenient steam drum connection to the filling tank.

5) Start filling the boiler with water 6590degC. While the feed water is being injected into boiler

through the regular feed system, start pumping the acid and inhibitor into the boiler through the

water wall header drains. If all the acid has not been pumped into the boiler by the time the

water shows in the gauge glass, secure feeding the boiler, until all the acid has been injected

into the boiler.

6) When all of the acid has been injected into the boiler continue to fill with water until the level in

the steam drum is high enough to cover all tubes to be cleaned. The tubes must be covered to

permit thermal circulation.

7) If it is desired to acid clean the entire drum completely fill the unit, adding acid in the same

proportions as before.

8) Run the circulating pumps 35 minutes each hour. If it is found that a wide temperature spread

exists between various parts of the boiler or if the scale deposit is excessive, use a half hour

cycle.

9) Check test samples of the cleaning solution with a standard sodium hydroxide solution and

methyl orange indicator. The value of this depends upon being able to get a true representative

sample. The acid concentration should be tested at the end of each circulation period. When

the concentration has leveled off, and remains constant over two successive tests the

dissolution can be considered complete.

10) Empty the boiler through the skin valve using compressed air.

11) Average acid contact time should be from 68 hours. If the scale has not been removed during

this period, the probable cause is:

a) Weak solution; repeat process.

b) Misidentified scale and wrong solution used, high in silicates, sulfates or oil.

6.11.3 General Precaut ions

1) Before injecting the acid solution into the boiler it is good practice to check the effectiveness of

the inhibitor. A weak inhibitor will permit excessive corrosion of the boiler metal.


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2) A quick check of inhibitor consists of diluting the concentrated acid to approximately 5 %, then

drop in a piece of cold rolled steel in the solution and heat to 65degC. Well mixed inhibited acid

produces very few hydrogen bubbles which should be small and difficult to see. For comparison

run a test with uninhibited acid.

3) Check the metal temperatures particularly the steam drum before injecting acid, before and

during each pumping operation. This can be done by using thermocouples located at critical

points or by contact pyrometer. It should be noted that THE TEMPERATURE IS A MOST

CRITICAL FACTOR in the procedure. Too low a temperature, under 50degC will result in poor

dissolution of most deposits. Too high a temperature, more than 80degC for most inhibitors, will

increase the corrosion rate appreciably, if not to a damaging degree. Stay within the

temperature limits prescribed by the manufacturer of the inhibitor. If there is any doubt, stay

under a temperature of 65 degC.

4) After draining out the acid, wash down the boiler with fresh water, using the same washing

process as described after boiling out.

5) The boiler should be boiled out with an alkaline solution (See Boiling Out). This is to both clean

the boiler of suspended particles and to return all surfaces to an alkaline base.

6) After boiling out, wash the boiler with a strong steam of hot fresh water with a hose.

7) After acid cleaning DO NOT ENTER OR WORK in the boiler until it has been filled at least once

with water, and preferably after the boiling out process.

6.12 Mechanical Waterside Cleaning

Whenever a boiler is opened, hose down accessible parts of the waterside. Water washing should not

be substituted for mechanical cleaning when latter is required.

6.12.1 Cleaning of Drums and Headers

nternals should be inspected whenever boilers are secured. Internal fittings should be removed from

the drum as necessary. Internal fittings should be carefully marked and identified as to position in the

drum to insure proper reinstallation. When above inspection indicates need for it, proceed with a

thorough wire brushing of all tubes and drums. The boiler should then be blown out thoroughly with

air, followed by washing out with water. Dry the boiler out and explore random tubes in all parts of the

boiler with a power wire brush. If dirty, repeat the cleaning process specified above.


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MAC Boiler Manual (Extract)

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Transcript of MAC Boiler Manual (Extract)