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Abstract
Coal-fired power plants need to respond to changes in electricity demand on diurnal, weekly, seasonal, and yearly time scales. The scale and frequency of these responses are forecasted to increase as levels of variable renewable energy sources become a larger part of the electricity supply. To respond to climate change concerns, it is also anticipated that the coal-fired power plants of the future will incorporate carbon capture and sequestration (CCS) technologies. Therefore, it is important to understand the dynamic response of coal-plants with CCS.

A variety of engineering studies have been published that investigate the energy penalty and design requirements for coalfired plant running at static power output and carbon capture rate of 90 percent; however, few of these studies explore the ability of the capture unit to respond to changes in load and capture rates. Noting that amine absorption is considered the most advanced near-term technological solution for carbon capture, this paper provides an analysis of the dynamics of a
MEA capture unit. This analysis enables the evaluation of the ability of coal-fired CCS power plants to provide load following support at different ramp rates and at varying levels of capture.

A dynamic kinetic model of an MEA capture plant was developed using Aspen Dynamics®. The model is used to determine the dynamic characteristics of the capture plant for load following by simulating various ramp rates of flue gas flow from the power plant to the capture unit. These results are used to determine the ability of the capture plant to control power output to the grid and the impact on performance parameters such as the capture rate and energy consumption. The results shown that the capture plant operates on similar time scales of a coal-fired power plant. The capture plant will not prohibit the ability of the coal plant to adjust output.

Introduction
Electricity generation from fossil-fuel power plants is one of the largest sources of carbon dioxide emisisons (IPCC 2005). To reduce the amount of emissions from these power plants, carbon capture and sequestration is seen as one of the most promising technology options. In particular, chemical absorption is the most widely studied and advanced subset of these technologies. To date, most studies have looked at the steady state, full load, 90% capture operation of the CCS unit
(Freguia et al. 2003; Abu-Zahra et al. 2006; Zhang et al. 2009).

Current coal-fired power plants need to be able to ramp to respond to changes in electricity demand and prices. If CCS is integrated into the power plant, it is important to determine the ability to respond to the changes in the power plant that may potentially affect the capture operation. Studies investigating load balancing with increasing penetration of renewables show that traditional baseload generation will need to be able to respond to a wide range of operating conditions and ramp rates (IEA 2011; GE Energy 2010). In addition, the operation of a flexible carbon capture system may enhance plant operating economics in by reducing steam required for solvent regeneration (Cohen 2011). Understanding the dynamics of the capture system is important for the operation of the power plant.