Well they do also use coal at drax but lets take the Biomass in isolation.
https://www.clientearth.org/the-greenwashing-files/drax/
"Drax’s burning of wood biomass has been found to produce higher levels of CO2 from smokestacks than its coal did, but these combustion emissions are allowed to be counted as ‘zero’ under international carbon accounting principles and EU and UK law, on the basis that any deforestation should be counted elsewhere, at the forest level." - they claim they will be carbon negative by 2030 but whatever their claim actually is the figures they are allowed to use and what they are allowed to omit make the whole thing a massive sham. "But scientists call into question the assumptions behind the carbon accounting: that forests are actually expanding, including because they are harvested, and that the ‘carbon payback’ from forest growth over decades will happen in time for urgent climate pathways. The climate impact of removing wood depends on the type – sawmill residues or logging by-product that would be burned anyway is not the same as the removal of trees or disturbance of soil which would otherwise capture carbon. However, felling trees for biomass energy can deplete forest carbon sinks." - essentially they have this "carbon accounting" method that is basically fraudulent accounting.