Appendix E - Coal-fired power plants: operating conditions and costs of carbon capture and sequestration

Summary

Basic elements of a complete end-to-end CCS system include CO₂ capture and compression, transport from the source to a repository, and monitoring the status of the sequestered CO₂ over time. Each element contributes to the total cost of CCS. Capture and compression costs increase with decreasing concentration and pressure of CO₂ in the gas stream from which it is extracted, while transport costs increase with increasing distance from the source to the storage site. Costs of monitoring the sequestered CO₂ are relatively small.

The cost of carbon capture for coal-fired power plants depends on the type of power plant, its efficiency, and whether the carbon is captured by pre- or post-combustion processes. To understand these options, it's helpful to first examine the makeup of a conventional plant. Consider the system shown in Figure E.1.

Pulverized coal (PC) and air enter the boiler, where the coal is burned to produce high-temperature products of combustion (POC). As the POC pass over tubes within the boiler (the steam generator), heat is transferred to pressurized water flowing through the tubes, converting it to steam. The steam is then routed through a set of steam turbines, where work is done on the turbine blades, enabling the turbine shaft to do work on an electric generator. To reduce losses in transmission by the grid, the voltage is increased by a transformer before the electricity enters the grid. The turbine has multiple stages to accommodate reheating in the boiler and to maximize the efficiency with which work is done by the steam. After leaving the last turbine stage, the steam is converted to water in a condenser and passed through a series of feedwater heaters and pumps before returning to the boiler to repeat the process.