Robin W. Hughes

Sintering and Reactivity of CaCO 3 -Based Sorbents for In Situ CO 2 Capture in Fluidized Beds under Realistic Calcination Conditions

Sintering during calcination/carbonation may introduce substantial economic penalties for a CO2 looping cycle using limestone/dolomite-derived sorbents. Here, cyclic carbonation and calcination reactions were investigated for CO2 capture under fluidized bed combustion FBC conditions. The cyclic carbonation characteristics of CaCO3-derived sorbents were compared at various calcination temperatures 700-925°C and different gas stream compositions: pure N2 and a realistic calciner environment where high concentrations of CO280-90% and the presence of SO2 are expected. The conditions during carbonation employed here were 700°C and 15% CO2 in N2 and 0.18% or 0.50% SO2 in selected tests, i.e., typically expected for a carbonator. Up to 20 calcination/carbonation cycles were conducted using a thermogravimetric analyzer TGA apparatus. Three Canadian limestones were tested: Kelly Rock, Havelock, and Cadomin, using a prescreened particle size range of 400-650 m. In addition, calcined Kelly Rock and Cadomin samples were hydrated by steam and examined. Sorbent reactivity was reduced whenever SO2 was introduced to either the calcining or carbonation streams. The multicyclic capture capacity of CaO for CO2 was substantially reduced at high concentrations of CO2 during the sorbent regeneration process and carbonation conversion of the Kelly Rock sample obtained after 20 cycles was only 10.5%. Hydrated sorbents performed better for CO2 capture, but also showed significant deterioration following calcination in high CO2 gas streams. This indicates that high CO2 and SO2 levels in the gas stream lead to lower CaO conversion because of enhanced sintering and irreversible formation of CaSO4. Such effects can be reduced by separating sulfation and carbonation and by introducing steam to avoid extremely high CO2 atmospheres, albeit at a higher cost and/or increased engineering complexity.

Waste Classification of Slag Generated in a Pilot-Scale Entrained-Flow Gasifier

Series of gasification tests have been completed in the pilot-scale entrained-flow slagging gasifier at CanmetENERGY using Canadian coals, oil-sand coke, and blends of these fuels to determine if the produced slags are nonhazardous in nature. Solid wastes generated during these tests were analyzed for their trace metals, crystallinity, and toxic constituent leaching tendency in an attempt to provide more insight into the possibility of disposal or by-product use of gasifier-produced solid waste. The gasification tests were performed at conditions representative of commercial gasifiers using a dry-fuel-feed configuration. The lower-volatility elements were found to partition between the slag and process-water solids (PWS) collected after gasification of the oil-sand coke. The less volatile group 1 elements tended to be enriched in both solid streams, whereas the slightly more volatile group 2 elements tended to exhibit higher enrichment in the PWS. Slag samples were found to be inert with regard to their leaching potential, and so these materials can be considered nonhazardous.

Hydration and Pelletization of CaCO 3 -Derived Sorbents for In-Situ CO 2 Capture

Steamhydrationandpelletizationoflimestone wereinvestigatedusinga thermogravimetric analyzer (TGA) toimprove the sorbent utilization for in-situ CO2 capture under typicalfluidized bed combustion (FBC)operating conditions. Steamhydration of CaO improves carbonation capacity but the hydratedsorbent is very fragile, which will be a problem for FBC applications. Similar sorbent improvements in terms of maintaining/enhancing reactivity were observed by sorbent fine grinding and pelletization, whichappears to be a method of using hydrated sorbent in fluidized bed applications.

High temperature monitoring of an oxy-fuel fluidized bed combustor using femtosecond infrared laser written fiber Bragg gratings

Femtosecond pulse duration infrared laser (fs-IR) written fiber Bragg gratings (FBGs), have demonstrated great potential for extreme environment sensing. Harsh environments are inherent to the advanced power plant technologies under development to reduce greenhouse gas emissions. The performance of new power systems are currently limited by the lack of sensors and controls capable of withstanding the high temperature, pressure and corrosive conditions present. This paper discusses fabrication and deployment of several fs-IR written FBG arrays, for monitoring the temperature distribution within a fluidized bed combustor. Results include: calibration data to ~ 1100 °C, discussion of deployment strategies, contrast with thermocouple data, and comments on reliability.

Entrained-flow gasifier and fluidized-bed combustor temperature monitoring using arrays of fs-IR written fiber Bragg gratings

Femtosecond written fiber Bragg gratings, have shown great potential for sensing in extreme environments. This paper discusses the fabrication and deployment of several fs-IR written FBG arrays, for monitoring main-spool skin temperatures of an entrained-flow gasifier, as well as the internal temperature gradient of a fluidized bed combustor.

Combustor deployments of femtosecond laser written fiber Bragg grating arrays for temperature measurements surpassing 1000 °C

Femtosecond Infrared (fs-IR) laser written fiber Bragg gratings (FBGs), have demonstrated great potential for extreme sensing. Such conditions are inherent to advanced power plant technologies and gas turbine engines, under development to reduce greenhouse gas emissions; and the ability to measure temperature gradients in these harsh environments is currently limited by the lack of sensors and controls capable of withstanding the high temperature, pressure and corrosive conditions present. This paper reviews our fabrication and deployment of hundreds of fs-IR written FBGs, for monitoring temperature gradients of an oxy-fuel fluidized bed combustor and an aerospace gas turbine combustor simulator.

Vanadium Oxidation State Determination by X‐Ray Absorption Spectroscopy

Vanadium is found in slags produced during metal refinement and fossil fuel combustion/gasification. The oxidation state of vanadium in slag has technological and environmental implications. For example, it may affect slag flow and refractory wear inside reactors, as well as leachability and toxicity of industrial by-products. Determination of vanadium’s oxidation state in crystalline phases can be achieved via the widely adopted X-ray diffraction (XRD) technique. However, this technique does not provide information on vanadium in amorphous phases. The objective of this research is to determine the oxidation state of vanadium in petroleum coke gasification samples and laboratory samples using X-ray absorption spectroscopy (XAS) with Canadian Light Source’s soft X-ray micro-characterization beamline (SXRMB). Linear combination fitting of XAS spectra with reference samples allowed quantitative determination of vanadium speciation.

Slag Surface Tension Measurements with Constrained Sessile Drops

Physical properties of slag are critical in the design and operation of refining technologies and slagging energy systems. The surface tension of slag impacts phenomena such as granulation, foaming, removal of solid inclusions, erosion of refractory and fouling. In this study, slag sessile drops formed on graphite, alumina and molybdenum substrates were compared. Use of graphite resulted in the largest contact angles, a desirable trait for surface tension measurements, but also led to reactions with the slag. Alumina and molybdenum were less reactive, but resulted in contact angles too small for measurements. When sessile drops were constrained by small substrate diameters to increase the apparent contact angle, surface tension measurements could be achieved with alumina and molybdenum substrates. The surface tension of coal slag was measured at up to 1600 °C in oxidizing and reducing gas atmospheres.

Understanding Phase Equilibria in Slags Containing Vanadium

In modern high temperature entrained flow gasifiers, the extensive use of petroleum coke (petcoke) as a replacement for or an addition to coal as a carbon feedstock introduces an appreciable amount of vanadium in the molten slag, resulting in unknown chemical and physical slag properties. A long-term research effort to understand phase equilibria of Al2O3-CaO-FeO-SiO2-V2O3 slag system representative of that commonly found in coal/petcoke carbon feedstock mixtures was initiated by the U.S.-DOE NETL. In collaboration with CanmetENERGY and McGill University, synthetic vanadium bearing slag was investigated for phases formed under controlled temperature, partial pressure of oxygen, and composition. The slag compositions representing U.S. and Canadian coal and petcoke ashes are considered in this work. Equilibrium phase diagrams of the vanadium slag systems are reported.

Role of the Water-Gas Shift Reaction in CO2 Capture from Gasification Syngas Using Limestones

The work in this paper aims at determining the effect of gasification syngas on the carbonation reaction and conversion for several naturally occurring calcium-based sorbents. Experiments were performed via the use of a thermogravimetric analyzer (TGA) and it was observed that the presence of CO and H2 caused an increase in initial rate of approximately 70.6%. The increase in reaction rate was attributed to the CaO surface sites catalyzing the water-gas shift reaction; as well, the shift reaction was assumed to be responsible for the increase in activation energy for limestone based on the formation of intermediate complexes.