J. Carlos Abanades

Post-combustion calcium looping process with a highly stable sorbent activity by recarbonation

This paper presents a novel sorbent regeneration technique for post-combustion calcium looping CO2 capture systems. The advantage of this technique is that it can drastically reduce the consumption of limestone in the plant without affecting its efficiency and without the need for additional reagents. The method is based on the re-carbonation of carbonated particles circulating from the carbonator using pure CO2 obtained from the gas stream generated in the calciner. The aim is to maintain the CO2 carrying capacity of the sorbent close to optimum values for CaL post-combustion systems (around 0.2). This is achieved by placing a small regeneration reactor between the carbonator and the calciner. This reactor increases slightly the conversion of CaO to carbonate so that it exceeds the so-called maximum CO2 carrying capacity of the sorbent. This increase compensates for the loss of CO2 carrying capacity that the solids undergo in the next calcination–carbonation cycle. Two series of experiments carried out in a thermogravimetric analyzer over 100 cycles of carbonation–recarbonation–calcination show that the inclusion of this recarbonation step is responsible for an increase in the residual CO2 carrying capacity from 0.07 to 0.16. A conceptual design of the resulting capture system shows that a limestone make-up flow designed specifically for a CO2 capture system can approach zero, when the solid sorbents purged from the CaL system are re-used to desulfurize the flue gas in the existing power plant.

CO2 Capture from Cement Plants Using Oxyfired Precalcination and/or Calcium Looping

This paper compares two alternatives to capture CO(2) from cement plants: the first is designed to exploit the material and energy synergies with calcium looping technologies, CaL, and the second implements an oxyfired circulating fluidized bed precalcination step. The necessary mass and heat integration balances for these two options are solved and compared with a common reference cement plant and a cost analysis exercise is carried out. The CaL process applied to the flue gases of a clinker kiln oven is substantially identical to those proposed for similar applications to power plants flue gases. It translates into avoided cost of of 23

In-Situ Capture of CO2 in a Fluidized Bed Combustor

/tCO(2) capturing up to 99% of the total CO(2) emitted in the plant. The avoided cost of an equivalent system with an oxyfired CFBC precalcination only, goes down to 16

On the climate change mitigation potential of CO2 conversion to fuels

/tCO(2) but only captures 89% of the CO(2) emitted in the plant. Both cases reveal that the application of CaL or oxyfired CFBC for precalcination of CaCO(3) in a cement plant, at scales in the order of 50 MWth (referred to the oxyfired CFB calciner) is an important early opportunity for the development of CaL processes in large scale industrial applications as well as for the development of zero emissions cement plants.

Capture of CO2 with CaO in a pilot fluidized bed carbonator experimental results and reactor model

Increasing atmospheric concentration of CO2 and concern over its effect on climate is a powerful driving force for the development of new advanced energy cycles incorporating CO2 capture. This paper investigates the feasibility of CO2 capture using the carbonation reaction of CaO “in situ” in a fluidised bed combustor, where natural gas or petroleum coke (or any other fuel with low ash content) is being burned. The sorbent can be partially regenerated for CO2 capture by combustion of part of the fuel with O2 /CO2 in a separate FBC. The thermodynamic limits in the proposed cycles, in terms of CO2 capture efficiencies, are examined along with the limits imposed by the rapid decay in the sorbent activity during repeated carbonation/calcination cycles, which will be exacerbated by the presence of S. Despite these limitations, it is shown that operating windows exist where it is possible to integrate fuel combustion, CO2 and SO2 capture in a single dual reactor facility. The decay in activity in the sorbent appears to be the major practical limitation to this concept, but this can be compensated for by using a relatively large supply of fresh sorbent, which appears to be acceptable considering the low cost of limestone. Also, a novel concept to reactivate the spent sorbent using sonic energy is outlined here as an alternative to reduce the use of fresh limestone.Copyright

Proof of concept of the CaO/Ca(OH)2 reaction in a continuous heat-exchanger BFB reactor for thermochemical heat storage in CSP plants

CO2 capture and conversion to fuels using renewable energy is being promoted as a climate change mitigation measure that reduces fossil fuel use by effectively recycling carbon. We examine this claim, first for a typical CO2 capture and utilization (CCU) system producing methanol (MeOH), and then for a generalized system producing fuels from fossil carbon. The MeOH analysis shows CCU to be an inferior mitigation option compared to a system with CCS producing the same fuel without CO2 utilization. CCU also is far more costly. The generalized analysis further reveals that the mitigation potential of CCU for fuels production is limited to 50% of the original emissions of the reference system without CCU. We further highlight that the main challenge to CCU cost reduction is not the CO2-to-fuel conversion step but the production of required carbon-free electricity at very low cost.

A Simulation Study for Fluidized Bed Combustion of Petroleum Coke With CO

Publisher Summary Experiments in a small pilot fluidized bed reactor have demonstrated that CO 2 capture from combustion flue gases can be effective at temperatures around 650°C as long as a sufficient fraction of CaO is present in the bed. The experimental CO 2 concentration profiles, measured in the interior and at the exit of the bed during the fast carbonation period, show that the fluidized bed is an effective CO 2 absorber even after several cycles. The axial CO 2 concentration profiles during the carbonation part of the cycle have been interpreted with the KL model, adopting reactivity data from previous work and sorbent deactivation data from laboratory tests. Once the model has been validated with experimental data, it allows an extrapolation to conditions beyond those tested during the experiments, in particular, conditions resembling the simultaneous generation (combustion) and capture of CO 2 (carbonation of CaO) which show that a compact CO 2 capture process can be designed with specific benefits for highly reactive fuel, like biomass.

Conversion limits in the reaction of CO2 with lime

The CaO/Ca(OH)2 hydration/dehydration reaction has long been identified as a attractive method for storing CSP heat. However, the technology applications are still at laboratory scale (TG or small fixed beds). The objective of this work is to investigate the hydration and dehydration reactions performance in a bubbling fluidized bed (BFB) which offers a good potential with regards to heat and mass transfers and upscaling at industrial level. The reactions are first investigated in a 5.5 kW batch BFB, the main conditions are the bed temperature (400-500°C), the molar fraction of steam in the fluidizing gas (0-0.8), the fluidizing gas velocity (0.2-0.7 m/s) and the mass of lime in the batch (1.5-3.5 kg). To assist in the interpretation of the experimental results, a standard 1D bubbling reactor model is formulated and fitted to the experimental results. The results indicate that the hydration reaction is mainly controlled by the slow kinetics of the CaO material tested while significant emulsion-bubble mass-transfer resistances are identified during dehydration due to the much faster dehydration kinetics. In the continuity of these preliminary investigations, a continuous 15.5 kW BFB set-up has been designed, manufactured and started with the objective to operate the hydration and dehydration reactions in steady state during a few hours, and to investigate conditions of faster reactivity such as higher steam molar fractions (up to 1), temperatures (up to 600°C) and velocities (up to 1.5 m/s).The CaO/Ca(OH)2 hydration/dehydration reaction has long been identified as a attractive method for storing CSP heat. However, the technology applications are still at laboratory scale (TG or small fixed beds). The objective of this work is to investigate the hydration and dehydration reactions performance in a bubbling fluidized bed (BFB) which offers a good potential with regards to heat and mass transfers and upscaling at industrial level. The reactions are first investigated in a 5.5 kW batch BFB, the main conditions are the bed temperature (400-500°C), the molar fraction of steam in the fluidizing gas (0-0.8), the fluidizing gas velocity (0.2-0.7 m/s) and the mass of lime in the batch (1.5-3.5 kg). To assist in the interpretation of the experimental results, a standard 1D bubbling reactor model is formulated and fitted to the experimental results. The results indicate that the hydration reaction is mainly controlled by the slow kinetics of the CaO material tested while significant emulsion-bubble mass...

CO2 Capture Capacity of CaO in Long Series of Carbonation/Calcination Cycles

Petroleum coke is regarded as a difficult fuel because of its high sulphur content and low volatile content. However, its low price and increased production, means that there is a powerful economic stimulus to use it for power generation. In this work, a process simulation has been performed as part of a feasibility study on the utilization of petroleum coke for power generation with low-cost CO2 capture. The proposed system employs a pressurized fluidized bed combustor and a calciner. In the combustor itself, the petroleum coke is burned and most of the CO2 generated is captured by a CaO sorbent under pressurized condition to form CaCO3 . The CaCO3 is transported into the calciner where limited proportion of the petroleum coke is burned with pure O2 , and calcines the spent sorbent back into CaO and CO2 . A nearly pure CO2 stream is obtained from the calciner for subsequent disposal or utilization. The predicted overall efficiency of the combustion is near 40%. The proposed system would also be suitable for firing other high carbon and low ash fuel, such as anthracite.Copyright