Fluidized Bed Combustion Systems Integrating CO₂Capture with CaO

Abstract

Capturing CO2 from large-scale power generation combustion systems such as fluidized bed combustors (FBCs) may become important in a CO2-constrained world. Using previous experience in capturing pollutants such as SO2 in these systems, we discuss a range of options that incorporate capture of CO2 with CaO in FBC systems. Natural limestones emerge from this study as suitable high-temperature sorbents for these systems because of their low price and availability. This is despite their limited performance as regenerable sorbents. We have found a range of process options that allow the sorbent utilization to maintain a given level of CO2 separation efficiency, appropriate operating conditions, and sufficiently high power generation efficiencies. A set of reference case examples has been chosen to discuss the critical scientific and technical issues of sorbent performance and reactor design for these novel CO2 capture concepts.

Durability of CaO–CaZrO3 Sorbents for High-Temperature CO2 Capture Prepared by a Wet Chemical Method

“…This corresponded to a CO 2 uptake of 0.19 g-CO 2 /g-sorbent in cycle 1, and 0.14 g-CO 2 /g-sorbent in cycle 15 showed CO 2 uptakes at cycle 10 of 0.31 and 0.36 g-CO 2 /g-sorbent, respectively. In contrast, the sorbents with a higher-Zr mass fraction had lower initial uptake but were more stable over multiple cycles, for example the uptake for 64wt%CaO36wt%ZrO 2 decayed from an initial value of 0.33 to 0.21 g-CO 2 /g-sorbent after 10 cycles 20 .…”

The impact of calcium sulfate and inert solids accumulation in post-combustion calcium looping systems

“…In the calciner coal burns under oxy-fired conditions [10] to attain the temperatures required to convert both the CaCO 3 from the carbonator and the fresh sorbent back to CaO (around 900ºC). Although the heat demand in this reactor (coal and O 2 ) is high [10][11], the overall energy penalty of the CaL process is low [10,[12][13][14][15][16][17][18][19], since energy can be recovered from high-quality heat sources (the solids streams between reactors, the carbonator and the high temperature gases abandoning the reactors). As a consequence of the nature of the CaL process, these systems have a continuous input of inert solids, mainly due to the coal fed into the circulating fluidized bed calciner but also because of the SO 2 in the flue gas entering the circulating fluidized bed carbonator.…”

“…The ratio between these two variables also determines the composition of the total inventory of solids in the system, which is known to affect the performance of the calcium looping process in terms of CO 2 capture efficiency and heat requirements in the calciner [11,[20][21]. Some previous works give an overall view of the CaL process by formulating the mass and energy balances of the whole system, and they analyze the performance of CaL under certain operating conditions, such as different make-up flows of limestone or different solids circulating rates between reactors [11,21], even in the presence of sulfur [12,20].…”

Carbon capture in molten salts

“…High-temperature post-combustion removal (HT-CCS) by carbonate looping has been identified by The European Technology Platform for Zero-Emission Power Generation (ZEP) as one of the most promising methods in the developing stage [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The concept relies on absorption of CO 2 by CaO with formation of CaCO 3 in the solid state.…”

“…The concept relies on absorption of CO 2 by CaO with formation of CaCO 3 in the solid state. CaCO 3 is subsequently stripped for CO 2 and CaO is regenerated by raising the temperature [4][5][6]. CaO is frequently chosen as the active substance in the solid-state carbonate looping system, but other alkali-earth metal oxides may be used similarly.…”