Why may boiler fuel consumption increase?

Owners and operators have increased fuel efficiency requirements nowadays. Any excessive fuel consumption may lead to complaints from charterer. Therefore, fuel consumption of main and auxiliary machinery should be closely monitored and any abnormalities investigated and rectified.
Almost any defect or incorrect operating procedure in the entire engineering plant is likely to be reflected directly or indirectly in a high rate of fuel oil consumption.

1. Sudden changes in steam consumption.

If steam demands change rapidly, some overfiring and underfiring of the boilers occurs with consequent waste of fuel. Sudden changes in steam consumption arise either from emergency operating conditions or from defects in the plant lineup or equipment.
1) Check for sudden changes in the ship's operating conditions
2) Check the lineup of the entire plant. Be sure all valves are open or closed, as appropriate
3) Check the operation of the main turbines and all steam-driven auxiliaries. Ensure that the throttle control is following the standard acceleration and deceleration tables.

2. Incorrect excess air settings

Too much excess air merely absorbs heat and carries it off through the stack, thereby wasting fuel. Insufficient excess air leads to incomplete combustion of the fuel, and this also results in high fuel oil consumption.

3. An incorrect relationship between the air pressure and the sprayer plates

Any condition which results in an incorrect relationship between the air pressure and the sprayer plates is wasteful of fuel oil. It may be caused by using sprayer plates of the wrong size, using mixed sizes of sprayer plates, setting the wrong air pressure for the condition of operation, other operational errors.

4. Low fuel pressure.

With low fuel oil pressure, it is impossible to achieve proper atomization and combustion. It is important to find the cause of low fuel oil pressure. Check following:
1) Temperature and viscosity of the oil
2) Operation of the fuel oil pump
3) A lineup of the fuel oil service system
4) Burner safety devices to be sure that the check valves or other safety devices are fully open.

5. Cold fuel oil

If the fuel oil is too cold when it enters the burners, it will not be atomized properly, combustion will be efficient. A larger amount of fuel oil will be required to generate a given amount of steam.
1) Check the fuel oil heaters
2) Be sure the drains are lined up properly

6. Burner failure

A number of burner defects lead to a poor fuel atomization, fuel impingement, soot or carbon deposits. 1) Check for worn or damaged sprayer plates, tips, nozzles, and atomizer barrels. See if the atomizer parts are clean.
2) Check the entire burners assembly for misalignments; in particular, see if the burner casing plates are warped, causing burner misalignment.
3) Check the air flaps to be sure they are clean and in good condition; be sure they are opened the correct amount when in use.
4) Check the impeller plates; if they are dirty or bent they will interfere with proper atomization.
5) Check the stationary airfoils for dirt or damage.

7. Dirty tubes, fire or waterside

Any factor that interferes with heat transfer is costly in terms of fuel oil consumption. Dirty firesides and dirty watersides cause serious interference with heat transfer and thus contribute very strongly to high fuel oil consumption.

8. Los feed water temperature

If the temperature of the entering feed water is lower than normal, more heat will be required to generate the steam. Consequently, more oil will be required to maintain the required rate of steam generation. Low feed water temperature is sometimes caused by incorrect operation of the deaerating feed tank. Another possible cause of low feed temperature is excessive recirculation of condensate.

9. Water contamination of fuel

Water in the fuel oil is wasteful because it interferes with combustion. A considerable amount of heat is required to evaporate the water, so more fuel must be burned in order to supply enough fuel for the boiler and enough to evaporate the water in the fuel.

10. Steam leakage.

Steam leakage is an obvious cause of high fuel oil consumption.

11. Leaky casings

Air leakage from the inner casing into the furnace interferes with combustion and thereby wastes fuel. Air leakage from the outer casing into the fireroom requires that the forced draft blowers be operated at a higher rate, thereby increasing auxiliary steam consumption and consequently increasing fuel oil consumption.

12. Too many steam consumers

The most economical way to operate the engineering plant is to use the minimum number of auxiliaries that will give the required results. Using more forced draft blowers than are actually needed is a common example of the waste of fuel by the use of too many auxiliaries.

13. Fuel leakage

Fuel oil leakage is an obvious-but often overlooked-cause of high fuel oil consumption. When checking the fuel oil system for leaks, do not forget to check for leakage at the burners.

14. Damaged refractories

Defects in the furnace refractories may make it impossible to maintain the necessary furnace temperatures without firing an excessive amount of oil and thus wasting fuel.

15. Auxiliary machinery defects

Defective parts in auxiliary machinery may increase the steam requirements for the machinery and thereby cause excessive fuel oil consumption. Worn bearings, defective governors, worn or excessively tight packing, scored or bent shafts and other mechanical defects cause auxiliary machinery to use more steam than would otherwise be required.