Solvent development and testing for post-combustion carbon dioxide capture

Abstract

Global warming is a significant problem presently. In its 4th Assessment Report the Intergovernmental Panel on Climate Change (IPPC) concluded that most of the observed increase in global average temperatures since the mid – 20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. Energy production and use has several environmental implications: since energy represents about 65% of global anthropogenic greenhouse gas emissions, reducing emissions must necessarily start with actions geared to reduce emissions from fuel combustion. Stabilising concentrations of greenhouse gases in the atmosphere would require large reductions of global CO2 emissions from the current levels. The energy sector is dominated by direct combustion of fuels, a process leading to large emissions of CO2. Worldwide economic stability and development requires energy. The global total primary energy supply (TPES) doubled between 1971 and 2007, mainly relying on fossil fuels. The emissions could lead to an increase in the earth average temperature between 2.4 and 6.4°C by 2100. (IEA, 2009). A possible solution of this problem could be the emission reduction of greenhouse gases before entering the atmosphere. As the volume of emitted CO2 is very large, significant financial and energetic resources are needed for its removal from flue gases. There are three main technological options for CO2 capture in the generation of electricity and heat: post-combustion capture through chemical absorption, pre-combustion capture, and oxyfuel processes (or denitrogenation). In one of the most promising ones, the post-combustion process, CO2 is captured from flue gases that contain 4% to 8% CO2 by volume for natural gas fired power plants, and 12% to 15% CO2 by volume for coal fired power plants. The CO2 is captured typically through the use of solvents and subsequent solvent regeneration. The basic technology (using amine-based solvents) has been used on an industrial scale for decades, but the challenge is to recover the CO2 with a minimum energy penalty and at an acceptable cost. (IEA, 2008)

One of the possible solutions to this problem could be to find new solvent systems with lower energy requirement in the stripping stage. The operational costs could also be reduced with stable chemicals resistant against degradation, with low volatility, high cyclic capacity and optimal operation.

According to the Kyoto protocol all Annex 1 countries have different quota of CO2 that can be released yearly into the atmosphere relative to their emissions in 1990. The countries can share this volume between the different industries considering the BAT (Best Available Technics). Exceeding the quota, results in financial penalties for the companies or countries. There are several possibilities to handle this problem from a company side, but of course the effort of cost saving - release the minimum CO2, and produce the maximum volume of product - is a big motivation for the companies from the oil, gas and thermal power plants to invest into this field all over the world. Another situation for CO2 capture is the “sweetening” of natural gas, where the acid gases are extracted to meet the contracted net calorific value and export specification of the natural gas. The CO2 capture is achieved in almost all cases by absorption into amine solutions which is the best economic method presently available to meet the quality and environmental requirements. The cyclic process consists of an absorber unit, where the CO2 absorption takes place and the desorber unit where regeneration of the absorbent happens, and where the CO2 is separated from the amine solution by heat energy addition and/or inert gas stripping.

The research presented in this thesis was carried out with the aim of improved solvent development and includes absorbent screening, characterization, and testing of the most successful candidates in a laboratory scale pilot plant.