safety valve unstable operation terms

     

Unstable Operation of safety valve

Unstable operation often results from misadjustment.

The following are the state of unstable operation and its remedy.

 Chattering

This is a rapid reciprocating variation in valve lift during which the disc repeatedly

contacts the seat. It is because popping power is weak. In this case, bring up

the lower ring (closer to the bottom face of the disc).

Hunting

This is the state where the disc repeats violent vertical motion during operation as if

it beats the seat violently. This is often caused when there is much flow restriction in the pipings connected with inlet and discharge side of the safety valve or when blowdown period is excessively too short. In this case, open the adjusting cook or throttle valve or bring down the upper ring to increase blowdown. lf hunting is not ceased despite the above adjustment, rechecking of the piping is necessary.

Fluttering

This is an abnormal reciprocating motion in valve lift during which the disc does

not contact the seat.

This is caused by the unbalance of the relative part against valve lifting power.

In this case, bring down the upper ring to increase the valve lifting power.

with canvas or the like to shut off the air.

economizer mounting, preperation,soot fire

       

Economizer installation

The exhaust gas economizer is designed so that it is installed on a strong installation base, and thermal expansion is absorbed by the long holes of the installation bolts provided in the base plate of the exhaust gas economizer.

As reinforcement against the ship's rolling, the structure can be supported by an anti-rolling fixture from the ship's side.

Gas inlet and outlet ducts are equipped so that the flow of gas comes in contact with the heating surface uniformly.

In a case where the inlet duct also serves as a dust catcher, it is provided with a large drain opening from which the washing water used for cleaning of the exhaust section can be discharged satisfactorily.

Cold Starting- of economizer

A CAUTION Before operating the exhaust gas economizer, following checks are to be made

 1. Check to see if the water supply to the steam separator drum (boiler or special-purpose

drum) is normally actuated.

2. Fully open all the valves between the evaporating part of the exhaust gas economizer and

the steam separator drum except the discharge valve of the circulating pump.

3. Open the air vent valve of the evaporating part header, and make sure that the drain valve

is closed and the root valve of the pressure gauge is open.

4. Operate the circulating pump.

5. Gradually open the discharge valve of the circulating pump.

6. Make sure that water spouts from the air vent valve of the evaporating part header, and

then close the air vent valve.

 Operation of Economizer

1. After preparations for operation, start the main engine and allow the exhaust gas to pass.

2. If the steam separator drum is not under pressure, open the air vent valve of the steam

separator drum, and when steam starts spouting, close the air vent valve.

3. When the pressure of the steam separator drum reaches the specified pressure, gradually

open the steam valve so as not to cause water hammer.

4. If the exhaust gas economizer includes a superheating part, open the drain valve of the

superheating part header to discharge all drainage.

Keep the air vent valve open.

When the exhaust gas temperature at the exhaust gas economizer inlet exceeds the steam

separator drum's saturation temperature under the specified pressure, gradually open the

superheating  inlet valve to allow steam to pass.

When steam starts spouting fiom the air vent valve, close the air vent valve, and finally

open the steam outlet valve gradually to begin normal operation.

SOOT FIRE [IMPORTANT]

The exhaust gas economizer operator is requested to take the following precautions to allow the

exhaust gas economizer to perform its full functions and for safe operation.

A CAUTION If soot is left adhering in the exhaust gas economizer, there is a strong

possibility that a soot fire (meltdown of heating tube) resulting from

soot burning will occur.

Soot will easily catch fire if the equipment is often used with the circulating pump stopped as when the ship enters and leaves port, during low speed operation (sailing on canal or river) or during

shifting, where a large amount of soot is generated.

Ifthe circulating pump is stopped, the cooling effect of the heating surface is lost, which will cause a serious accident leading to a meltdown of the heating tube (s).

Since a soot fire is an accident which should occur least, make every effort to prevent soot, one of the three burning elements, from adhering.

1. Scot is generated by incomplete combustion of the main engine, and is affected by the fuel,

handling of it, conditions of the main engine, combustion of lubricating oil, etc. A large

amount of soot is generated especially when the load on the main engine has dropped and

when the supercharger has been cleaned.

2. Adjusting the main engine in good condition is the method for preventing soot from

adhering, and strict observance of soot-blowing and water-washing when the ship is

anchored are methods for removing soot.

Soot-blowing is effective in removing unadhered soot, but it cannot totally compensate for

poor operation of the main engine. Soot which cannot be removed by soot-blowing should

be removed by water-washing when the ship is anchored.

Handling a soot fire

Soot that catches fire is detected by the exhaust gas high temperature alarm (if

available) or another method such as sparks coming out of funnelincreased economiser back pressure. the following emergency measures are taken immediately.

1.       Bypass the exhaust gas (if a bypass device is available at the exhaust gas pipe

side). If it cannot be bypassed, stop the main engine, and cover the air suction port

with canvas or the like to shut off the air

2.       Continue the operation of the circulating pump. If possible operate both pumps in

parallel. (Lower the temperature in the exhaust gas economizer.)

3.       Continue the operation of the circulating pump. If possible operate both pumps in

parallel. (Lower the temperature in the exhaust gas economizer.)

Do not operate the soot blowers. Also, if soot-blower is operating, immediately

stop it.