Biomass powerplants are thermal powerplants for the most part. There have been some drawn up to run on the methane production from biomass decomposition but to my knowledge they haven't been put into commercial production.
Biomass fuels burned include agricultural wood, forest wood, urban wood, miscellaneous ag shells, pits and pomace, straws, and stalks. The advantage, of course is using renewable resources and getting some heat value out of them without just throwing it all away.
The problem is getting consistency in fuel and availability to power a large powerplant. Most powerplants designed around coal are only economical because the coal is consistent in heat value and size and so can have equipment that handles it properly for burning efficiency and waste removal. Plus coal powerplants are usually in the 1000's of megawatt capacity and so their cost per watt charge is very low.
Biomass, because the fuel is varied and not usually available in train car amounts, has powerplants in the 5-100 megawatt capacity. You just can't generate power economically in this small amount because of the capital cost for equipment is so large in comparison to the amount of power you produce. For example, it might cost 100 million dollars to generate 100 MW of power, but if you generated 5000 MW of power, the equipment cost might be 300 million dollars, but you get 500 times more power from only 3 times the capital cost. Plus coal is virtually unlimited.
Biomass has a hard time competing unless there is a huge supply of a single source material, like sawdust or corn stalks or something. But for a mechanical engineer to try to design a boiler that burns sawdust one day and then corn stalks another day, it is very difficult to process different fuels to burn cleanly and efficiently in the boiler.
If you are still interested, here are some used complete systems for sale. As I said, the biggest downside to these is their small generation size compared to the huge coal burning facilities. You can generate a KW-H of electricity at a large (5000+MW) coal plant for around 4 cents a KW-H.
To generate a KW-H of power in a relatively large biomass plant (30+MW) , will cost about 12 cents a KW hour or more. The economics are hard to get around.