Page 50: of Maritime Reporter Magazine (November 1981)

Upgrading Of The

Shipboard Boiler Plant (continued from page 46) in the area of 15 to 20 million dollars per ship. This is a sizable investment when you are looking for a quick payback on your out- lay. I believe the advantages of converting to coal, even when you consider that reboilering is re- quired, far outweigh the diesel conversion approach.

On coal firing, history points out that this is not something which is new; we are simply im- proving on existing technology.

Major improvements have been made in the last 30 years in met- allurgy, design and manufactur- ing techniques used in modern marine boilers, as well as the fuel- burning fuel-handling systems employed.

The coal-fired marine plant will utilize a readily available and eco- nomical stoker coal. Present day prices, February 1981, place stok- er grade coal at $2,201 per mil- lion Btu versus oil at $5.20 per million Btu. The prices based on dollars per million Btu equate to $212 per ton for bunker "C" oil and $55 per ton for stoker-grade coal.

The economics, based on a 20,- 000-shp plant operating 300 days a year at rated power, show that the oil-fired plant consumes 173.75 million Btu per hour. This translates into $6,505,200 per year. The coal-fired plant would consume 180.00 million Btu per hour, which represents an annual cost of $2,851,200. Thus, the fuel cost savings by using coal would be $3,654,000 per year.

The added cost for the coal- fired plant with coal bunkers, fuel and ash handling equipment is estimated at $3,000,000 per ship above that of an oil-fired steamship. Obviously, any invest- ment that can be written off in less than four years is well worth investigating.

The classification of coal under consideration for marine applica- tion today is stoker-grade bitu- minous, which is still available in numerous areas of the United

States and the world for marine bunkers.

A present-day land coal-fired boiler generally consists of a com- bustion system which burns pul- verized coal in suspension in the furnace, or stoker-fired units which burn coal on a fixed or moving grate system. Coal-fired utility boilers generally use pul- verized coal systems simply be- cause a stoker cannot accommo- date the huge quantities of fuel consumed.

Coal pulverizers and the burner system are generally designed for a specific coal. This does not pre- sent a problem for land-based plants. Marine bunkering coals, however, will vary in specifica- tions and may not be acceptable to a pulverizer system as origi- nally designed.

We, therefore, feel that a stok- er-fired boiler is the best present- day solution for coal firing aboard a vessel. The stoker will more readily accept changes in the fuel specification which are likely to occur in marine coal bunkers.

The main shipboard coal bunk- ers proposed are of the hopper- bottom type. Transportation of the coal from the extraction point at the main bunker to the day bunker can employ one of two basic systems available. One sys- tem is mechanical and the second is a pneumatic transport system.

The mechanical coal feed system configuration can vary depending on the machinery space layout.

It is estimated that a reboiler- ing conversion to coal-firing units would be in the five to seven mil- lion dollar range. This includes removal of existing boilers, in- stallation of all new equipment, plus an insert into the hull struc- ture for coal bunkers.

In conclusion, in a world which is subject to liquid fuel prices rising uncontrollably and with rapid degradation of liquid fuel, coal is a viable alternate for shipboard application.

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