CONTROLLING POWER PLANT CO2 EMISSIONS: A LONG RANGE VIEW

Abstract

ALSTOM Power (ALSTOM) is an international supplier of power generation with concern for the environment. We are aware of the present scientific concerns regarding greenhouse gas emissions and the role of fossil fuel use for power generation. Although the scientific and policy dialogue on global climate change is far from conclusive, ALSTOM continues to invest in R&D to develop: high efficiency power generation equipment with the most modern technologies to utilize fossil fuels with the lowest possible emissions (short, medium and long term) term), and technologies to remove and sequester carbon dioxide created in power plants in an environmentally and economically favorable manner (long term). This paper is an overview of activities to study and develop controls for carbon dioxide (CO2) emissions from power generation. First, energy efficiency improvements for both new and existing fossil fuel power plants are briefly reviewed for both coal and natural gas fuels. Greater depth is then given to options for CO2 capture and sequestration. These studies are looking at current and novel power generation technologies. CARBON DIOXIDE EMISSIONS FROM FOSSIL FUELS When greenhouse gas emissions are under discussion, CO2 is generally the gas which receives the most attention for its greenhouse effect. Although the radiative forcing of CO2 is much less than other greenhouse gases (CH4, N2O, CFCs, etc.), CO2 is emitted in large amounts into the atmosphere and has a rather long atmospheric lifetime. When all these parameters are modelled, with our current state of knowledge, to evaluate the global warming potential, CO2 is estimated to contribute approximately 60% of the enhanced greenhouse gas effect [1]. The exponential growth of the global economy since 1860 has been based on fossil fuel consumption. During this period, mankind has collectively released approximately 950 billion tons of carbon dioxide (260 Gt of carbon) from the burning of oil, coal and natural gas [2]. These fossil fuel emissions have been increasing at an average rate of 2% a year to a 1997 annual global output of around 23 billion tons of carbon dioxide (6.3 Gt of carbon) (Figure 1a). Roughly half of these emissions (3.5 Gt of carbon) remain in the atmosphere, the rest being adsorbed by natural processes [3]. CO2 concentrations have increased by 35% from the pre-industrial 280 parts per million by volume (ppmv) to the current 370 ppmv (Figure 2). Coincident with these changes, the global average temperatures have increased by almost 1°C at the surface of the earth. Figure 1a: Historical evolution of CO2 emissions [4] Figure 1b: CO2 emissions by source and by type [2] Figures 1a and 1b: CO2 emissions from (fossil) fuel combustion Climate scientists argue that in order to stabilize these rising concentrations and temperatures, reduction in CO2 emissions of 60 to 80% may be required [5]. Figure 2a: CO2 concentration over the last 400 000 years [6,7] Figure 2b: CO2 concentration over the last 150 years [7, 8] Figures 2a and 2b: CO2 atmospheric concentration The 1997 CO2 emissions picture for the four principal sector sources by fuel used are shown in Figure 1b. Since fossil fuel-fired power plants exist at fixed locations, they are easier to 32% 25% 23% 20% 43% 19% 38% 1997 total CO2 emissions from fuel combustion (23.0 Gt in 1997) Elec. & heat Prod. Manufacturing Transport Others by Sector by Fuel