Composite boiler exhaust outlet temperature rises along with increased fuel consumption for same load.

Composite boiler exhaust outlet temperature rises along with increased fuel consumption for same load.

Particulars

Machinery: Alborg Composite Boiler.

Pressure jet burner: KBO-R25M

Operating module: Alfa Laval (Retrofit)

Tube type: Pin tube

Only one servo motor for air fuel ration.

(No separate SIPART for air damper)

Ship type VLGC

Details:

The boiler burner is in manual continuous firing mode at 45% load (lowest load) but we manually lowered it to 42% now.

Ship was at anchor for almost the last six months. Every week we were cleaning the smoke side with compressed air only.

Recently we noticed that at same boiler load and same air-damper notch the following occurred:

1. Smoke density increased.
2. Fuel consumption increased for the same load.
3. Increasing the air-damper notch to supply more air reduced the smoke density to approximately 0%, but the exhaust gas temperature increased drastically.
4. Reducing the air supply caused the smoke density to increase while the exhaust temperature decreased.

Even after water washing it is rising @ 2~3⁰C per hour.

0600 hrs - 288⁰C

1000 hrs - 301⁰C.

Observations:

1. When smoke density is less than 3% - exh temperature rises.
2. When smoke density is 6-7% - exh temperature stays same
3. When smoke density is over 7% - exh temperature drops.

We have been using shore water with high chloride levels near to 500 for the last 6 months. So scaling of water surfaces is a possibility.

Also, tried reducing fuel pressure to 21 bar. No change.

There is one servomotor which controls fuel regulator along with air damper. Fuel regulator and air damper cam is fixed in same shaft. No separate controller for air.

Measures taken:

Burner nozzle already replaced.

Fuel oil pressure is 23bar. (Before it was 24 bar, we reduced it after this issue)

Fuel oil temperature is 110⁰C.

We cleaned smoke side with water.

Parameters (Normal/Present): Exhaust temperature

1. Before - around 315⁰C.
2. Now - 345⁰C & rising fast.

Present Status: Still temperature is rising at 2~3°C per hour.