Cofiring Project Phases
In general, the following are the steps to consider and implement in a co-firing project:
Fleet/multiple unit screening The generation portfolio is reviewed, including conventional and renewable energy sources, to benchmark GHG emissions. Units that can most contribute to the companys climate action plan when co-firing with RPS eligible biomass are identified.
Fuel supply study Reliable co-firing is contingent upon the supply and characteristics of biomass. This study identifies options for a secure, predictable supply from source to the power plant stockpile. Also, pre-processing of woody biomass (such as pelletizing) can strengthen the supply infrastructure and reduce transportation costs; these options are investigated.
Preliminary technical/economic assessment The preliminary assessment looks at the power plants suitable for co-firing. An initial ranking is performed based on location, transport and storage infrastructure, boiler design layout and size while considering economics.
Detailed technical/economic assessment The detailed assessment further analyzes the ranked set of power plants technically and economically, taking into consideration the detailed design, characteristics, operating experience, and configuration to further refine the return-on-investment and technical changes required.
Conceptual design This phase provides a high level design for a specific plant, including the overall plant architecture and layout plans. The biomass injection route is selected during this phase.
Detailed design The detailed design includes an analysis of technology and equipment suppliers, details all interface points and provides work scope packages to perform the adaptation to co-firing.
Implementation This phase provides the project management and governance programs to ensure a successful project.
Operation and monitoring In this phase, the project is fully implemented, and now the fine-tuning is performed with appropriate diagnostics and calibration. Also, a corrosion monitoring and prevention program is established.
In general, there are four alternative approaches to injecting biomass into the generation process. Each approach targets different parts of the process, as shown in Figure.
These approaches can be summarized as follows:
Approach 1 blends the coal/biomass mixture on a conveyor belt and co-mills the fuel mixture in the existing coal pulverizers, then combusts in the existing coal burners.
Approach 2 separates biomass pre-processing (milling and drying), followed by injection of the biomass in the pulverized fuel lines (after the pulverizers) and simultaneous biomass/coal combustion in the original or modified coal burners.
Approach 3 separates biomass pre-processing and feeding and combustion in separate, dedicated biomass burners.
Approach 4 provides for indirect co-firing of biomass; for example, through an upfront gasifier with co-combustion of the (cleaned) fuel gas in the main coal-fired boiler.