Soot Blow
Purpose To remove soot, to prevent EGE fire To get steam generating efficiency good To increase heat transfer efficiency
Time Day time at sea 2 -3 times/day Procedure Inform to bridge
Check wind direction, good it transverse direction Raise boiler pressure
Open drain cock until drain clear Open soot blower valve
Open steam valve & carried out by turning wheel 20 -30 sec Then close steam valve, soot blower valve
Boiler safety valve closed examination and attention during overhauling
Checked its valve and valve seat for wear, cavity corrosion and any fault. They should be grounded properly but maker’s limit must be maintained such as width of seating, clearance between valve lip and seat.
Valve chest must be cleaned condition and drain line clear.
The spring should be hammer tested for any fracture and check for corrosion. Free length is limited to 0.5 % of original free length.
The spindle should be hammer tested for any crack and its straightness.
The guide plates and bushes are checked for uneven wear and have sufficient clearance to allow free movement of spindle.
The compression nut and cover bush’s threads are carefully checked it for any sign of wear and tear.
The easing gear should be checked in good order including bearings, cable pulley, and connecting links.
Connecting pin should be a free fit in the lid (
tzHk:
) and pin should not bent or pinhole gone out of shape.All safety valves are to be set to operate under steam a little above working pressure not greater than 3% above the approve working pressure of the boiler.
Why safety valve is fitted in two numbers ?
To make sure that the positive discharging of higher steam pressure from boiler efficiency. Why fitted in one valve chest ?
To reduce stress by hole on pressure vessel (boiler)
1. What is emergency air compressor ?
It is a small compressor independently driven by diesel engine or hand operated.
It must be fitted to press up the emergency air bottle and to start auxiliary engine of a dead ship. It has no connection between the main air bottle.
2. Air compressor safety devices ?
******
1 Bursting discs are fitted on the cooler shells (At water side). 1 Relief valves are fitted to discharge side for every stages. 1 Moisture drain valve (unloader) are fitted at each cooler side 1 Cooling water failure alarm.
1 Low L. O pressure alarm.
1 Delivery air high temperature alarm on after cooler outlet (Max 93°C)
LP discharge pressure 4 bars : HP discharge pressure 30 bars. Intercooler inlet air 130°C : Intercooler outlet air 35 °C After cooler inlet air 130°C : After cooler outlet air 35°C
Intercooler is single pass type : After cooler, double pass U-tube type
3. Purpose of unloder valve (moisture drain valve) ?
At starting this valve must be opened, this reduced the starting torque for the machine and clear out any accumulated moisture and oil in the system.
4. What would be affect of suction valves of an air compressor having too much lift ? The valve will be late in closing and this would reduce the volumetric efficiency of the machine .The valve too much lift reach at the end of their travel will grater force and therefore are more liable to break.
5. Affects of reduced volumetric efficiency of air compressor ? Grater bumping clearance.
Sluggish opening and closing of suction and delivery valves. Insufficient cooling water that effect of high air temperature. Dirty or partially chocked suction air fitter.
6. Different between relief valve and bursting disc ? Pressure relief valve
@ Excess pressure is released by opening the valve. @ It opens at 10% over working pressure.
@ Valve lift is proportional to excess pressure build up. @ Valve setting pressure can be altered by spring tension.
Bursting disc
Pressure is released by bursting the disc. It permanently damaged.
It burst at setting pressure.
Fusible plug
When the temperature high (above 105
°
C) Pressure is released by melting (fusing) the metal.It cannot be used next time. ( permanently damage) Release all content or pressure to empty.
7. Why multistage compressors are mostly used than single stage compressor ? @ More stages are needed to increase the required final pressure.
@ Easier to control the air temperature. @ Reducing in air compressor size. @ Lubrication problem does not exit. @ Reduced the thermal stress.
@ Lower work done to compressing air. @ Improve compressor efficiency
8. Advantages of inter cooling of air compressor ?
To avoid excessive temperature rise associated with higher compression ratios, and to approach isothermal compression.
Saving in power.
Volumetric efficiency is increased.
Reduced the volume of air delivered and also reduced the compressor size. It can reduce the air temperature.
Due to less temperature suction & delivery valves remain cleaner without being fouled with carbonized oil.
It can avoid a danger of an explosion takes place in compressor cylinder. It allows good lubrication of the compressor piston.
Moisture separation is easier through inter cooler drains.
It also enables to deal with a greater wt of air for the same energy expended.
Why intercooler will fitted in Main air compressor?
1. Reduced air temperature, volume and increased air density for next stage 2. So increased Volumetric efficiency and compressor efficiency.
3. Due to reduced temperature give better lubrication for cylinder and piston rings
4. Drain are fitted from which water and excessive oil can be drained out, to prevent air bottle corrosion and starting air explosion and fouling of inter coolers and pipe.
5. Save the work done.
Advantages of after cooler purpose
To reduce final discharge air temperature thus air bottle seize can be reduce. To reduce air volume after it has been compressed to the final pressure. So greater amount of air could be stored in air bottle.
Increase volumetric efficiency
9. How to start the air compressor manually ?
@ Change the switch to manual position on the switch board. @ Check the L.O sump level and condition.
@ Open the moisture drain valve.
@ Open the compressor discharge valve & charging valve of air bottle. @ Open cooling water system valves.
@ Check the pressure gauge readings. @ Frequently drain the moisture.
@ When charging full, open drain valve and stop the compressor
10. How do you check compressor efficiency @ running ?
a Checked by filling time with the previous record and also check the first stage discharge pressure. If
compressor efficiency is lower, compressor will run longer and compressor temperature will rise. a First stage and second stage pressure gauge must be correct and stabled
a No escape air from suction filter
a Intercooler and after cooler outlet air temperature should not be high a If open drain valve nothing can found
a Low L.O consumption
a Oily air mixture must not blow out from breather pipe. 11. Safety devices on main air bottle ?
@ Pressure relief valve.
@ Fusible plug.(if safety valve is not directly fitted on the bottle) @ Pressure gauge.
@ Low air pressure alarm. @ Moisture drains valve.
12. Where is the fusible plug fitted ? Purpose ?
Fusible plug is fitted under side of the pipe between relief valve and air bottle.
It is fitted to release the compressed air in the event of abnormally high compressed air temperature. Fusible plug melt at 105
°
C and release all content of air. It is made by 50% Bismut, 30% tin, 20% lead.A fusible plug is fitted after the second stage cooler to limit the delivered air temperature and thus protect the compressed air reservoirs and pipe work.
13. Can you fit the relief valve at the space of bursting disc and why ? *****
At the compressor, relief valve can not be fitted at the bursting disc, because of their difference operation.
Bursting disc is fitted for totally release and stop operation circuit.
Release valve opens excess pressure at compressor running and reseat at when pressure reduce or when the compressor is stopped. Thus cooling water can enter to compressed air space; it can cause water hammer when the next start of compressor.
14. What is volumetric efficiency ?
It is the ratio of the actual volume of air drawn in each suction stroke to the stoke volume.
Volumetric efficiency =