How Do Steam Plants Use Different Fuels?

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Historically it wasn't uncommon for boilers to be run on fuels different from those they were originally designed for. Ships were commonly converted from coal to petroleum after the 1910s, and for a period of time it was common to convert power plants from coal to petroleum as well. A common feature then and now is the use of petroleum to help start coal fired power plants or improve their burning of coal. After the energy crises of the 1970s and the increased cost of petroleum many power plants were converted to coal, including some that were originally designed to burn petroleum. Some steam plants were built to run on natural gas as well.

I haven't been able to find a diagram of anything other than a coal fired steam plant and I haven't been able to find any information on what exactly is done to change a power plant between fuel types. Does anyone know what kind of modifications are done to allow the different fuel types to be burned? Are there any diagrams of steam plants in different configurations?
 
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Oil to gas is easy; you just change the burner. It's basically just a flamethrower that bolts over a hole at the bottom of the boiler.

Coal to oil would be more complicated because of how much space a burning bed of coal takes up.
 
I can't say that I've seen conversion project plans, but I think I can outline the steps.

  1. Add fuel handling to bring the fuel to the furnace. Coal pulverizers can be eliminated.
  2. Add burners of appropriate size (this is what @russ_watters mentioned. (By the way, coal is blown into the furnaces as a fine dust, not burned in beds.) Also, igniters need to be appropriate.
  3. Each burner must be dynamically adjustable to match the original proportions of heat to furnace/superheater/reheater sections.
  4. Weld shut the wet bottom of the furnace (where coal slag was removed).
  5. Adjust the primary and secondary air fans to provide enough air without wasting fan power.
  6. Remove/bypass the bag house and precipitators from the exhaust end used to catch flyash from coal.
  7. Re-calibrate and re-tune the boiler control systems.
  8. Re-design safety and startup/shutdown logic.
  9. Evaluate safety contingencies.
  10. Re-program the training simulator (if any) and retrain the operators.
In some cases, like in the NYC area, they are required to fuel with oil or gas with rapid switching between fuels. That means dual fuel systems.

Edit: add re-design control room panels.
 
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russ_watters said:
Coal to oil would be more complicated because of how much space a burning bed of coal takes up.
anorlunda said:
In some cases, like in the NYC area, they are required to fuel with oil or gas with rapid switching between fuels. That means dual fuel systems.
And coal requires pulverizers and fans to blow the dust into the boiler. Totally different fuel handling than oil or gas which are pumped in pipes right to their respective burners.

Our fossil units burned oil or natural gas (when we could get it) or a mix. We didn't have coal in Florida.
The analog pneumatic control system controlled the flows of both fuels into the burners, and positions of dampers inside the boiler. Gas with its blue flame has less radiant heat than oil's yellow-orange flame so the gas gets routed a little differently through the superheaters.. .[/QUOTE]