Carbon dioxide (CO_2) reduction has become a key objective around the world and thepower industry has a big challenge to meet the reduction targets. This objective is moredifficult to achieve in the countries such as the United States where a large portion ofgenerated power is already based on coal combustion. Many technology companies arecontinuing their long-term development for CO_2 capture technologies and several largecoal burning utilities have begun to pilot test these technologies. Examples of thesetechnologies are CO_2 chemical and physical absorption as well as oxygen richcombustion in order to make CO_2 capture easier. The basic technologies for these arewell-known, however, there are still many challenges to be solved before thesetechnologies are commercially available.Another common approach is to increase the efficiency in steam cycle to decreasespecific CO_2 emission per produced kWh. Increased steam pressure and temperaturecombined with supercritical technology in CFB, may increase the efficiency 10 %, forexample from 40 to 44%, meaning 10% less CO_2 emission per kWh.A third approach to the same topic is to burn zero CO_2 net emission fuels, like biomass.However, biomass introduces new technical challenges including bed agglomeration andhigh temperature corrosion. One way to manage this effectively is to gasify the mostchallenging fuels and burn the easier ones in fluidized bed boilers. Burning the biomasstogether with coal makes the chemistry much easier to handle.Metso Power has demonstrated experience providing coal and biomass co-combustion inCFB boilers. In Scandinavia the thinking was to make biomass fired CFB with coal backup.In coal dominant countries it could be reversed, coal is the base fuel and biomass isburned as and when it can be purchased from local markets. This paper introducesseveral operating co-combustion projects from size 50 MW_e up to 250 MW_e discussingabout fuels, the chemistry and operating challenges as well as requirements for boilerdesign and equipment.Metso Power is developing all the technologies mentioned above, but biomass co-firingwith coal is really the only one which is commercially available today without any realtechnical drawbacks.
展开▼
