This isn't greenwashing if it's sourced from waste. That's CO2 that would have entered the atmosphere anyways, was originally sourced from the atmosphere by plants, and burning it actually skips the 20 years it would have spent as methane which is 80x more potent as a greenhouse gas than CO2, making it actually a benefit. No new carbon is being released as is the case with fossil fuels. Is this scalable to the entire energy economy? No, is it a sustainable use of a byproduct of waste in place of carbon adding fossil fuels? Yes.