Analys av designalternativ för snabbare dynamik i kolkraftverk med koldioxidavskiljning

Sammanfattning: Combustion of fossil fuels is today the dominating source of energy. During combustion,carbon dioxide is formed. The carbon dioxide accumulates in the atmosphere,which raises the global average temperature on earth through the so called greenhouseeffect. The only way to reduce the emissions of carbon dioxide from combustionin a coal fired power plant is through carbon capture and storage (CCS).Post-combustion capture is a technology to separate carbon dioxide from the uegas after the combustion for efficient transport and storage. The steady state operationof coal fired power plants with post combustion capture has already beenthoroughly investigated on a pilot scale, however much work remains to investigatethe plants dynamic operation. Due to the increasing amount of intermittent energysources, such as wind and solar power, the energy system will require that theplants that run as base load today will be able to rapidly respond to changes in load.The present work investigates the operation of a coal fired power plant with postcombustion capture during load changes. The response rate for different design optionshas been evaluated and discussed with respect to possible operating scenarios.The investigation does not include economic estimations, even though the importanceof capture cost is discussed.According to the modelling it takes 90 to 105 seconds to reduce the electrical outputfrom a power plant with CCS with one percentage point, depending on whichload the change is made from. A coal fired power plant without the CCS technologyis approximately eight times faster than a power plant with CCS. To increase theresponse rate of a post combustion system, a method for partial capture of the carbondioxide was investigated. This method is referred to as CFCC (Constant Fluegas Carbon Capture). This option separates a constant amount of carbon dioxideregardless of the power plant load. In this case the system with CCS will changethe load as fast as a power plant without CCS because the amount of ue gas andsteam will be kept constant. This option is favorable when the power plant runs onlow loads most of the time and increases the load to cover for the peaks in electricitydemand. In this case the amount of carbon dioxide captured is less affected by thereduced capture capacity.Another option that was investigated was to temporarily stop the capture unit byreducing the steam extraction to the separation plant to improve the power plantresponse rate, a method referred to as EDCC (Emergency Dumping of Carbon Capture).In that case a lower degree of separation was accepted during the load changes,making it possible to follow the increased demand on electricity. With this methodit is possible for a power plant with CCS to make a load change faster than a powerplant without CCS. To stop the capture unit is the fastest way to make a loadchange of all investigated options. Reducing the steam drain to the separation plantfor the short period of time required for the power plant to increase in load has onlya slight effect on the overall capture rate.