the steam esteem questions and answers.doc

8/10/2019 The Steam esteem Questions and Answers.doc

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You are welcome to ask any relevant questions.

Please, share your know-how and contribute with answers to the visitors' questions. We

have all different experiences and no one knows everything, but together we can solve lotsof problems. n easy question for you might be a hard one for a colleague or vice versa.

Question: Boiler pressure

!n tanker vessels we use boilers for cargo heating."ets say that steam pressure to deck line ad#usted to $ bar.

What will be most economical% &oiler pressure ad#usted to bar or to () bar %

Answer:

*he higher pressure would be advantageous if the boiler is oil-fired,but the difference is hardly measurable.

!f you have a diesel engine exhaust gas economi+er then bar boiler pressure would gainmore heat from the exhaust gases.

Question: Emegency low water level in the boiler

! want to know what should be my immediate action in case ! saw no water in the boiler

gauge glass.

Answer:

top the burners immediately.

o not pump in any feedwater until you know that the boiler is undamaged.!f some parts of the plates or tubes are glowing, then increasing of the water level will

cause an enormous evaporation and hence a pressure rise that the safety valves can'tmanage and an explosion might be a fact.

Question: Cavitation in a two flow line

We have a steam generating facility using process heat. *he condenser is a verticalcondenser with process vapours on tube side and boiler feed water on shell side. *he outlet

of the shell side is a two phase flow. Pipe thickness reduction of the shell side outlet pipe is

observed for last couple of years. We replace the piece of pipe every one year. ! want toknow the probable reasons for this to happen.

Answer:

! guess it might be a cavitation problem. alculate the flow rate. ecreasing the speed of

the flow might be a solution i.e., increase the pipe diameter
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Question: Boiler rum level control goes haywire

We are having (// tones 0& boilers. 0requent problem observed is that whenever there is

sudden load change the boiler drum level control goes haywire leading to tripping of boilerand turbine on drum level low or high. 1ur drum level control is 2-element control in auto

mode.

Answer:

*he most common fault with a three-point level controller is the steam flow transmitter."oosen the impulse pipes and cleanse the holes into the measuring orifice.

Question: !iring light crue oil

an a 3ain &oiler built to fire 24/ cst 501, be fired with light crude oil directly from thecargo-tanks%

Answer:

completely new fuel system is required, from deck to the burner rails of the boiler. *o

prevent any possibility of gasses leaking from flanges, there have to be ducting enclosingthe entire fuel-system with forced draft fans that vent 2/ times the volume of the trunking

to the outside. lso there have to be a burner hood to be constructed all over the burner

roof, equally vented. 6aturally there have to be new burners and so is the burnermanagement.

*here are two main contractors who are capable and willing to carry this out7

53W18*59-ombustion :ngineering in ;< and


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!n the old days some ships sailing on lakes used the lakes water as make up water for their

boilers, but even that water caused problem with salt in the boilers although it is supposedto be fresh-water.

Question: #eavy fuel oil viscosity

5eavy fuel oil viscosity is defined in the standards as the viscosity at (//B yet the oils areoften described in terms of their nominal C/ or $/B temperature viscosities. e.g. a =2$ oil

@2$cst at (//BA is often described as anything from a 2$/cst to 2>/cst oil. 8efineries blend

to control the viscosity at (//B. *esting aboard ship or in boiler hosues appears to test the

viscosity at $/B. &ecause of the variation in quality of the residual oil and distillate thatmake up a heavy fuel oil, it is difficult to make a good correlation between the $/B and

(//B measurements. 3y question is, how is the blending of oil in the terminals or on fuel

barges controlled% and how reliable is this in achieving the required viscosity%

Answer:

*he values you get from my 0uel 1il alculation program are normally sufficient for firing

a boilers heavy fuel oil burner. 0or a diesel engine on the other hand, ! assume that an

automatic viscosity-controller would be indispensable.

Question: #eating up a fire$tube boiler

!s there a minimum temperature that a fire-tube boiler should reach before going to a high

fire state to prevent tubes from leaking%

Answer:

*he important thing is to heat up the boiler slowly so all parts of the boiler expand #ust as

much. *he leaks occur when some part expands more, or less, than the rest of the boiler.

9ou will be on the safe side if you slowly heat up the boiler to, or almost to, normaloperation pressure before you start high firing.

Question: Combustion air preheating

Please tell me how air inlet temperature affects boiler efficiency. What are the benefits ofair preheating%

Answer:

*he combustion air will be heated to the flame temperature. *his heating cost money. !f

you have some waste heat to be used for preheating the combustion air it will pay.


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Question: %ater in the heavy fuel oil

!s it possible to overheat heavy fuel oil thus causing any water in it to turn to steam and

cause problems at the pump and burner%.

Answer:9es it is. *he temperature of the heavy fuel oil is very often (2/B to ($/B and water

introduced to that temperature would immediately evaporate into steam. When boiling it

expands about ($>/ times. *he situation might be dangerous since the safety valves not aredesigned for steam.

*his kind of problem is very likely to occur when you change fuel oil tank and some water

from a poorly drained pipe mixes with the heavy fuel oil.

Question: &il showing in the water level gauge glass

Whilst on your engine room rounds, you discover oil showing in the water level gaugeglass of an auxiliary boiler. escribe the remedial actions you would take, explaining why

such actions must not be delayed.

Answer:

top the burner immediately.

1il present, even small quantities, in boiler water will cause foaming and moisture carry-over. !t also forms a heat insulating film, sometimes a carboni+ed layer, over tubes or shell

surfaces. :ven a very thin layer may result in tube or plate material failure due to

overheating.

*he oil manifests itself by forming an oily ring inside the water gauge glasses, at the water

level.

Question: Emergency low boiler water level

9ou are an officer on watch, D finds the boiler water-level gauge glass to be empty D theburner firing...What is your course of action% @ssuming the gauge glass to be clear D

good working orderA

Answer:

6ormally a boiler is provided with two independent sensors for emergency low water level

burner cut-outs. o this would never happen. 5owever, if it does, donEt take any chancesFhut off the burners immediatelyF

&efore you start raising the level in the boiler you have to find out if any part of the furnacewalls has been overheated. !f you raise the level over a glowing steel-wall then the boiler

might produce more steam than the safety valves can handle and a nasty explosion would

be the result.

quick test to see if it is safe to put water into the boiler is to temporarily close the steam


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cock on the gauge glass. !f the level rises to the top of the glass, it means that there is still a

water level in the water leg, which is also over the highest heat exchange surface in a

firetube boiler. *he water rises because of the vacuum caused in the glass with condensingsteam.

Question: 'ifferential pressure transmitters for the steam rum level

Way is the high pressure leg of the transmitter connected to the water side and the low-pressure leg connected to the steam side%

Answer:

*he signal from the transmitter ought to increase when the water level raises and decreases

when the level falls. 0urthermore the signal shall be +ero, and give impulse to stop theburner, in case of transmitter malfunction, power failure or cable breakdown.

&oth requirements will be fulfilled if the transmitter is mounted with the high pressure

measuring point connected below the lowest water level and the low pressure measuring

point connected above the highest water level. *he output will increase when the level israised. *o compensate for the water column in the reference leg the output signal's +ero-

point has to be elevated.

*his is the common method.

!f the transmitter is swapped, with the low pressure side to lower end and the high pressureside to upper end, then the signal will decrease when the level is raised.

*his signal can be used to control the level as well, but the signal can not be used to stop

the burner for emergency low level in case of power failure or cable breakdown. *hissystem requires an extra sensor to trip burner at emergency low water level.

1ne can of course use the emergency high water level alarm to stop the burner, but this is

not correct. *he emergency high water level shall stop the feed water pump and wheneverapplicable stop the steam turbine, but not the burner.

Question: !luctuating boiler water level

*he feed water control valve is fully open and the water levels fluctuate at normal boiler

load.

Answer:

heck if7

the control valve really is fully open by means of the hand-manoeuvre device.

all stop valves in the line are fully open.

the suction filter to the feed water pump is satisfactory clean.

the feed water pump discharge pressure is sufficient.


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the feed water control valve pressure drop is normal. @GHI bar or GH2/ psiA

!f all these are fund to be in order, then you should recalculate the control valves


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Answer:

!f you have a one liter of water standing in the pipe #ust after the valve and open the valve

too fast, then you will get a pro#ectile of one kg rushing down the pipe. t next valve, bendor other obstacle the speed of the water mass will be converted into pressure. 9ou can

hardly imagine the damage this energy can cause.*hermal stress is an other reason to be very cautious and drain out water carefully whenyou open a steam valve.

large steam valve ought to have a small by-pass valve to simplify preheating of the pipe.

Question: *ow viscosity fuel for high viscosity burners

1ur boiler plant is designed to be fired with heavy fuel oil of $>/ ct K $/B.Would it be safe to run it on =as 1il of ct K C/B%

Answer:Well, this is a question for the burner maker. Don't forget to ask them too.

!t is outmost important that the fuel oil heaters are by-passed when firing =as 1il or iesel1il. *hese fuels must never be heated above their flash-point.

0or a steam atomi+ed burner you have to switch over to compressed air atomi+ing

since light fuels must not be atomi+ed by means of steam. *his burner will probably

fire the fuel without any problem since they normally are designed for fuel viscositybetween (/ and I/ ct.

rotary cup burner, on the other hand, might give some problem with the flame

since this atomi+ing method normally require a fuel viscosity of about I$ to )/ ct.

!n the event of failed ignition, gas-oil is more likely to cause an explosive mixture thanheavy oil. 5owever, a dangerous situation should never occur if the procedure for such

failed ignition is followed. ;pon two consecutive failed ignition attempts, a thorough

investigation into the cause should be sought and the furnace correctly purged inline withthe manufacturers and ruling classification societyEs requirements.

6.&. ct K C/B H $.$ ct K $/B.

*he viscosityEs of lighter fuels are normally given at C/B and the viscosity of heavier fuels

at $/B, 4/B, (//B or even higher temperature.0or conversion of viscosity and density at one temperature to viscosity and density at an

other temperature ! recommend *he 0;:" 1!" alculation Program.

Question: !uel &il +gnition Quality, CCA+

What is the ! of a fuel oil%

Answer:
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*he !, the alculated arbon romaticity !ndex, is a measure of the 0uel 1ils !gnition

Luality.

*he value can be calculated using the following, !1 4I( nn., formula7! H -4(-(C( "og(/"og(/@ J


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of problems.

Question: (ransport superheate steam!s it possible to transport superheated steam of the order of C$ tNh at 2/ bar pressure andtemp of 2// deg from a aux boiler to a distance of (.$ ftNsA. *o avoid water hammering the pipe-line

should slop slitely downwards in the steam flowing direction. *o start up the line you willneed a drain valve on every 2/ m @(// ftA.

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