Appendix CanmetENERGY G A Final Phase IV Report … · A Final Phase IV Report Prepared by CanmetENERGY, August 2014 ... the Development of Oxy-fuel Circulating Fluidized Bed Combustion

C a n a d i a n C l e a n P o w e r C o a l i t i o n : A p p e n d i x GG01

Appendix

GCanmetENERGYA Final Phase IV Report

Prepared by CanmetENERGY, August 2014

Table of Contents

1. R&D Activities to Support a Comprehensive Evaluation of Potential Beneficiation Technologies _________ G02

1.1. Coal Drying Process Characterization ____________________________________________________________ G02

1.2. Predicted Properties of Slag Generated from Beneficiated Coals ____________________________________ G02

2. The Scientific and Engineering Basis for Advancing Calcium Looping Cycle Technology

from Pilot Scale to Demonstration Scale _________________________________________________________ G03

2.1. Calcium Looping Combined With Chemical Looping Combustion ____________________________________ G04

3. Experimental and Modeling Activities to Support the Development of Short Residence Time Gasification _ G04

3.1. Slag and Inorganic Element Science _____________________________________________________________ G04

3.2. Dry Fuel Feeding ______________________________________________________________________________ G06

3.3. Gasification Modeling _________________________________________________________________________ G07

3.4. Gasification Process Integration and Control ______________________________________________________ G08

4. Experimental Activities to Support the Development of Oxy-fuel Circulating Fluidized Bed Combustion ___ G08

Figures and Tables

Table 1: Slag characteristics by coal type ____________________________________________________________________________ G02

Figure 1: CanmetENERGY dual fluidized bed pilot-scale facility __________________________________________________________ G03

Figure 2: Fuel delivery, fuel dispersion, and gasifier arrangement ________________________________________________________ G06

Figure 3: Image of solid fuel being injected from a gasifier burner at ambient temperature and 15 bar(g) pressure using a high speed camera _________________________________________________________________________________ G06

Figure 4: Initial gasifier simulation shows strong upward flow near the burner, opposing incoming petroleum coke and nitrogen _________________________________________________________________________________________ G07

Figure 5: Preliminary results for char reactions (left) and temperature (right) give a rough indication of the size and position of the flame __________________________________________________________________________________ G07

Figure 6: Gasifier slag model results: (left) particle deposition profile and (right) slag layer thickness in the upper portion ________ G08

C a n a d i a n C l e a n P o w e r C o a l i t i o n : A p p e n d i x G G02

1.1. Coal Drying Process CharacterizationTest work has been performed at CanmetENERGY to establish the performance and power plant implications of coal drying technologies. A small pilot unit (10 cm ID, ~ 200 cm in height) has been used to dry coal and characterize the produced vapour, condensate and dried coal. The pilot unit has been operated to emulate waste heat utilization (WTA) drying technology and DryFining drying technology.

Two temperatures were used for the test work. Temperature 1 (55°C) required low grade heat commercially that was extracted from waste heat streams with relatively low capital investment requirements. This temperature was sufficient for removing surface moisture, but insufficient for substantial inherent moisture removal. Temperature 1 is similar to the temperature of operation of Dryfining technology.

Temperature 2 (115°C) required steam extraction and/or more substantial capital investment in using waste heat streams commercially. The higher temperature was suitable for the removal of a substantial portion of inherent moisture. Temperature 2 is similar to the temperature of operation of RWE’s WTA technology.

Three coals were considered in the test work: Highvale sub-bituminous, Boundary Dam lignite and Poplar River lignite.

A study of the kinetics of coal drying was performed to determine the effect of drying temperature and particle size on the rate of coal drying to create a UniSim® model of the process. The kinetics of coal drying were studied under a nitrogen environment, with plans to continue the work with dry and humid air. Kinetic expressions were developed, dependent upon the drying temperature and the particle size of the coal being dried.

1.2. Predicted Properties of Slag Generated from Beneficiated CoalsProperties of slag (density, surface tension and viscosity) were modelled based on data from Sherritt’s GAMS report for various beneficiated coals. A summary of the results is presented below, indicating the changes between the feed and beneficiated fuels for each coal and property combination.

Table 1: Slag characteristics by coal type

Coal Slag Density (kg/m3) Slag Surface Tension (mN/m) Slag Viscosity

Poplar River Small reduction Small increase ~50 No change

Boundary Dam Small increase Large increase ~200 Large decrease at T<1600 K

Highvale Small increase No change Moderate decrease at T<1800 K

Genesee Small increase, ~50 No change Moderate decrease at T<1800 K

The change in ash composition could result in lower operating temperatures for slagging equipment, such as oxy-fired IGCC facilities and oxy-fired combustors, hence improving the efficiency of these systems for the Boundary Dam, Highvale and Genesee coals.

CanmetENERGY

1. R&D Activities to Support a Comprehensive Evaluation of Potential Beneficiation Technologies

Gas Analysis

Stack

FUEL HOPPER

LIMESTONE HOPPER

WATER COOLED FEED SCREW

WINDBOX

RECYCLE BLOWER

BAGHOUSERETURN LEG

CFBC CYCLONE

CONDENSER

Drain

Primary O2 /

Mixed Gases

Secondary O2

Air

WINDBOX

EDUCTOR

CALCINER / COMBUSTOR

Air / Recycle Flue Gas

DIVERTER VALVE

Air

KO VESSEL

CARBONATOR

ELECTRIC BOILER

STEAM SUPERHEATER

SOLIDS TRANSFER

AUGER

Solids to CFBC

Solids from BFB

BFB CYCLONE

Air

SOLIDS TRANSFER CYCLONE

CONDENSER

BAG FILTER

Flare / Stack

Gas Analysis

Manual Solids Loading

Air / CO2 /

Simulated or Real Flue Gas


2. The Scientific and Engineering Basis for Advancing Calcium Looping Cycle Technology from Pilot Scale to Demonstration Scale

CanmetENERGY’s pilot-scale dual fluidized bed facility was renovated and successfully commissioned in the summer of 2013 to test solid looping cycles for CO2 capture. The facility has the unique ability to operate in full oxy-fuel mode with flue gas recycle (either wet or dry), allowing for production of a flue gas stream with a CO2 concentration greater than 90 per cent.

Figure 1: CanmetENERGY dual fluidized bed pilot-scale facility

A test campaign with continuous CO2 capture and various levels of steam in the oxy-fired calciner was completed in the pilot plant using calcium based sorbents. The calciner was operated with steam concentrations of 0 per cent, 15 per cent and 65 per cent at the inlet of the windbox. The increase in steam in the calciner decreased the fresh sorbent make-up rate; for instance, a 78 per cent reduction

in make-up was observed with 65 per cent steam in the calciner. In commercial operation, the increase in steam concentration could be achieved by taking a slip stream of low quality steam from the steam cycle or by operating a wet flue gas recycle system, depending on the desired extent of dilution.


2.1. Calcium Looping Combined With Chemical Looping CombustionScenarios have been studied to evaluate carbon capture and storage (CCS) applications including post-combustion CO2 capture and pre-combustion biomass gasification, with chemical looping combustion, as well as sorption-enhanced reforming for hydrogen production with simultaneous CO2 capture.

Calcium Looping (CaL) is a developing technology for reduction of CO2 emissions from power plants using fossil fuels for electricity production that is being intensively examined. However, the production of the required oxygen for sorbent regeneration is costly, as typical cryogenic air separation units are highly energy intensive and expensive to build. Chemical looping combustion (CLC) could replace oxy-fuel combustion via the use of a metal oxide acting as an oxygen carrier (such as copper(II)-oxide, CuO), which provides the oxidant for burning the fuels required in the sorbent regeneration stage. The integration of the two technologies could result in a higher net efficiency and lower capital cost for CCS as cryogenic air separation is not required and the CO2 stream is oxygen free.

The feasibility and performance of integrated calcium-chemical looping pellets were with three types of structures, i.e., integrated CuO core-in-CaO shell pellets; integrated homogeneous CaO/CuO pellets; and mixed CaO and CuO pellets.

The mixed pellets appear to be more promising than those of integrated pellets due to their relatively better performance. Additionally, mixed pellets are easier to produce with good quality control than core-in- shell pellets.

3. Experimental and Modeling Activities to Support the Development of Short Residence Time Gasification

3.1. Slag and Inorganic Element ScienceSlag viscosity models are applied in many industries. However, the models are only applicable to a limited range of slag compositions and conditions, and their performance is not easily assessed. During this phase of work, CanmetENERGY published a journal paper that described the tools that were developed to assist slag viscosity model users in the selection of the best model

for given slag compositions and conditions. It also helped users determine how well the model would perform. The tools, which are in the form of several publicly available files and programs, include a slag viscosity prediction calculator with 24 slag viscosity models, and a database of 4124 slag viscosity measurements. The database includes more than 750 compositions from 53 published studies. New slag viscosity models, integrated into the tools, include an artificial neural network for fully molten slags, and a viscosity prediction modifier for slags containing solid particles. Glass forming, entrained flow gasification and blast furnace case studies were developed to demonstrate how the slag viscosity modeling tools can be applied and to highlight certain features that should be considered when using slag viscosity models and experimental data.

Petroleum coke may be used as a fuel for entrained-flow slagging gasification. It may be blended with coal to provide a more attractive feedstock. The coal provides the benefits of enhancing reactivity and increasing the amount of slag coating the gasifier walls, while the petroleum coke increases the heating value of the fuel blend. The slagging behaviour of the petroleum coke or blend must be known to determine if it is a suitable feedstock. During this phase of work CanmetENERGY published a journal publication providing results on the slag viscosities of coal, petroleum coke and coal/petroleum coke blends measured in the temperature range of 1175 – 1650°C. Two different viscosity measurement apparatuses were used in separate laboratories (CanmetENERGY and CSIRO in Australia). Some viscosity measurements were repeated to test reproducibility of the results. Also, slags with and without sulphur were tested to determine whether the effect of sulphur can be neglected.

Slag chemistry is important for the assessment of flow behaviour of slags produced during gasification of coal and coal–petroleum coke blends. Slags containing vanadium species react readily with the crucible and spindle materials used for viscosity measurements. Interaction of vanadium-rich slags with various materials has been investigated in collaboration with CSIRO in order to obtain a better understanding of the impact of containment materials on the resulting slag chemistry and viscosity. The bulk and phase compositions of two petroleum coke slags in Al2O3, Mo, Pt and Ni crucibles produced under different laboratory conditions were analysed, and kinetics of slag composition changes at 1400°C were determined.


Mechanisms of the slag interactions with crucibles were determined. They involve exchanging of crucible and slag constituents, formation of interfaces with distinct compositions, and continuously changing phase equilibria in the system. For slag processed in Ni and Pt crucibles, reduction of Fe and Ni from oxide to metallic form occurs and is followed by dissolution into the crucible materials. Viscosity of slags with Mo, Ni and Al2O3 crucibles are determined in the temperature range 1200-1500°C. Resulting changes in the bulk composition of the processed slag has an impact on the slag viscosity. At given temperatures, viscosities of the slags produced in different crucibles are different. The impact of crucible materials and their applicability in viscosity measurements of high vanadium-containing slags have been determined in order to define the optimal conditions.

In entrained flow gasifiers, non-volatile impurities from feedstocks form liquid slag, contributing to degradation of the refractory liner and potential slag flow issues. To understand thermodynamics of the slags, NETL and CanmetENERGY investigated phase equilibria in synthetic slags (Al2O3-CaO-FeO-SiO2-V2O3) corresponding to industrial coal/petcoke feedstock blends in simulated gasifier environments. Samples were equilibrated at 1500°C in a CO/CO2 atmosphere (pO2=10-8 atm) for 72 hours, then analyzed by ICP, XRD, SEM-WDX and TEM. With increasing CaO and FeO contents, the homogeneous slag phase field was found to expand, while the phase field containing mullite (Al6Si2O13) became smaller. The effect of high vanadium content (up to 20 wt.%) on the phase stability was determined. Pseudo-isothermal phase diagrams based on the equilibration experiments have been generated on CaO-V2O3 coordinates.

Physical properties of slag, such as viscosity, density, interfacial tension, heat conductivity and heat capacity, are important for mineral processing, metal processing, slagging combustion and slagging gasification. In the case of slagging gasification, slag properties will impact the efficiency, reliability, maintenance cost and environmental performance of the overall process. The majority of the inorganic matter (i.e. oxides of elements excluding hydrogen, carbon, nitrogen and sulphur) present in the fuels will deposit on the reactor hot face as liquid or semi-liquid slag. The slag will flow down into a quench zone and be collected as solidified slag. Within the

gasifier, slag coating can decrease heat transfer, which may or may not be desired in the process, and also protect or corrode the hot face. In some cases the slag is too viscous and can lead to reactor plugging issues if corrective actions, such as temperature increases, fuel blending or flux addition, are not taken. Notably the wear of refractory and plugging issues are two of the greatest concerns in the gasification industry. CanmetENERGY developed methods to measure slag density and interfacial tension during this phase of work by applying the sessile drop technique with a tensiometer. Three different image analysis software packages were evaluated: SCA20, LBADSA and ADSA.

A suite of emerging IGCC technologies provide the promise of both high efficiency and reduced capital costs. Many of these operate at elevated temperature and hence a number of inorganic elements (i.e. elements other than C, H, O, N and S) may be present in the syngas at later stages of processing than is typical of conventional processing arrangements. CanmetENERGY analyzed experimental results for inorganic element distribution in slag and fly ash from seven entrained-flow slagging gasification plants. Data for the Siemens, Louisiana Gasification Technology Inc. (LGTI), Wabash River, ELCOGAS and Shell gasification systems were taken from literature. Data for the CanmetENERGY and Pratt & Whitney Rocketdyne (PWR) systems were presented for the first time. Mass balances and enrichment factors were calculated. Challenges in data interpretation and general trends were highlighted. Mass balance closures for low volatility elements are within the range of 80 to 120 per cent for the PWR, LGTI and Shell systems. Closures for the CanmetENERGY, Wabash River and ELCOGAS systems are further from 100 per cent. Accumulation, unaccounted streams, measurement inaccuracy and sampling imperfections can cause poor mass balance closures. Comparison of enrichment factors for slag and fly ash demonstrate that many elements have similar fates in gasification systems as they do in combustion systems, although several elements are less volatile in gasification systems. Partitioning can vary for a given element when comparing different gasification systems and different operating conditions. The assessments of several elements that are of environmental or technological concern were provided as examples.


3.2. Dry Fuel FeedingFigure 2: Fuel delivery, fuel dispersion and gasifier arrangement

During this phase of work CanmetENERGY extended their optical spray techniques for use with dry feeds being injected in high pressure vessels as shown in Figure 2. In order to optimize control of dense-phase conveying systems, an understanding of the system and particle fluid properties affecting the flow behaviour is required. In order to do this, two existing models of dense-phase conveying were evaluated: the Sprouse and Schuman model (1983) and the Geldart and Ling model (1990). These models were compared to experimental data using the dense-phase conveying system at CanmetENERGY and three pulverized solids: biomass (sawdust), lignite coal and petroleum coke. These solids were chosen as they have different particle properties, and they are potential fuels for use in the Canadian gasification industry. It was found that the Sprouse and Schuman model was a good representation of the petroleum coke and coal flows, while the Geldart and Ling model was less representative. Laser sheet visualization of biomass sprays was conducted in the cold-flow, high-pressure spray characterization vessel. A pulsed laser was used with a high-speed camera to capture “freeze-motion” images of the particles, providing almost instantaneous snapshots of the spray along the cross-section of interest. The edge detection technique was successfully used to determine spray edges.

Figure 3: Image of solid fuel being injected from a gasifier burner at ambient temperature and 15 bar(g) pressure using a high speed camera


3.3. Gasification ModelingA computational fluid dynamics (CFD) model of short residence time gasification is being developed. A validation of the modelling approach is underway, based on experimental petroleum coke gasification tests performed at CanmetENERGY on the pilot scale entrained flow gasifier in September 2013. The geometry and mesh for the model are complete and include heat transfer through the solid refractory liner and the walls of the burner for a short distance upstream of the inlet. A separate simulation of flow through the burner was done to estimate a heat transfer boundary condition where cooling water flowed through the burner. These results are being applied to the main gasifier model.

Figure 4: Initial gasifier simulation shows strong upward flow near the burner, opposing incoming petroleum coke and nitrogen

Figure 5: Preliminary results for char reactions (left) and temperature (right) give a rough indication of the size and position of the flame

Slag deposition, flow, and corrosivity are key phenomena that affect the heat transfer and reliability of the reactor. Therefore, a validated slag flow model is a useful tool for the design of these systems. CanmetENERGY developed a model that includes ash deposition, running slag flow and immobile slag layer formation. The ash deposition is determined from a computational fluid dynamics (CFD) model of the reactor. This model was applied to the operation of the CanmetENERGY entrained flow gasifier and compared to the operational measurements, which included slag layer thickness and reactor wall temperatures. The effects of uncertainty in key parameters were investigated.


Figure 6: Gasifier slag model results: (left) particle deposition profile and (right) slag layer thickness in the upper portion

3.4. Gasification Process Integration and ControlA comprehensive literature review was conducted on the recent state-of-the-art technologies, sensor placement methodologies, dynamic performance and control strategies that have been proposed to improve the efficiency of Integrated Gasification Combined Cycle (IGCC) processes. Technologies and configurations including different types and designs of membranes, short residence time gasifiers and new classes of turbines with higher firing temperature represent promising economically attractive technologies for IGCC power plants and therefore are thoroughly reviewed in this work. Optimal sensor placement is critical since harsh operating conditions within specific IGCC components and budget constraints do not allow installing sensors that measure some key process variables for this system. The statistical approaches to determine the optimal number of sensors and their location in the plant were discussed. The dynamic performance of IGCC processes in closed-loop control was considered under critical scenarios (e.g., transient behaviour of the processes under load changes) using various tools, such as plant-wide and local control strategies, and process assessment under uncertainty. Furthermore, challenges and development potential for optimal sensor location and control systems for commercial IGCC power plants were outlined in this work.

4. Experimental Activities to Support the Development of Oxy-fuel Circulating Fluidized Bed Combustion

Oxy-fuel combustion technologies are increasingly being considered a viable option for reducing CO2 emissions from coal-fired power plants. While most research activities in this field have been focused on applying oxy-fuel technologies to pulverized coal (PC) combustion, in the past several decades it has been recently recognized that circulating fluidized bed combustion (CFBC) are an alternate technology that could be adapted for oxy-fuel combustion. In fact, CFBC has some advantages as compared to PC for oxy-fuel combustion that may make it a better choice as a CO2-capture technology. For example, by using an external heat exchanger(s) in the return-leg, a great deal of bed temperature control can be realized, facilitating higher oxygen concentrations than can be used safely in pulverized coal oxy-fuel combustion. This high allowable oxygen concentration could enable oxy-fuel CFBC units to operate with lower flue gas recycle ratios in comparison to PC oxy-fuel combustors, which leads to significant improvements in terms of operating costs. In order to conduct research on oxy-CFBC technology, CanmetENERGY has operated pilot-scale 0.05 and 0.8 MWth oxy-fuel CFBCs for several years and some of the works conducted with these units contributed to Foster Wheeler’s Ciuden oxy-CFB demonstration unit.


Compared to PC combustion, CFBCs have the added benefit of being able to handle a wide variety of fuels. They are able to efficiently and easily combust materials such as biomass, municipal solid waste and other waste solids. Due to the favourable emission profiles of certain biomass materials, CFBCs can also co-fire coal and biomass to achieve improved combustion performance, as well as economics.

To reduce flue gas recycle ratio and the size of the combustion chamber, high oxygen concentration oxy-fuel CFBC combustion has been proposed. It is anticipated that oxygen concentrations of up to 50 per cent in the combustion gas mixture could be used during oxy-fuel CFBC operation, provided an external solids heat exchanger was integrated into the return-leg. Under these conditions, the flue gas recycle split could be reduced to about 50 per cent. Comparing this value to oxy-fuel PC systems, which have flue gas recycle splits of 75 to 80 per cent, there is a considerable potential for savings. These savings are realized through minimizing the size of the recycle blower and the cost reduction in piping systems.

To develop high oxygen concentration oxy-fuel CFBC technologies, combustion characteristics of several types of fuels can be first examined via TGA (thermogravimetric analysis) testing under simulated high oxygen concentration oxy-fuel CFBC environments. Oxygen concentrations of up to 50 per cent by volume were tested using several fuels such as bituminous coal, anthracite, lignite and petroleum coke. Ignition temperature, burn-out time and overall apparent activation energy was determined for each fuel under varying conditions.

The results indicated that up to 900°C, the rate of CO2/carbon direct reaction is negligible for these fuels, and CO concentrations in a CFBC boiler under oxy-fuel conditions should be similar to those as observed during air-fired operation.

In 2013 and 2014 a series of tests were conducted firing Canadian fuels (Poplar River, Boundary Dam, Genesee, Highvale and Suncor Petroleum coke) using the 0.05 MWth oxy-CFBC pilot plant with high concentrations of oxygen in the fluidizing gas. The purpose of the tests was to demonstrate oxy-CFBC firing at high oxygen concentrations (up to ~ 40 per cent O2 in fluidizing gas) and to generate validation data for process simulations and computational fluid dynamics modeling of the combustor. The tests were intentionally performed at bed temperatures that would result in both direct and indirect sulphur capture pathways. Direct sulphation is expected under oxy-PFBC conditions. Of special interest in these tests was the dramatic capture of SO2 in the lignite tests under direct sulphation conditions. All coal fired tests were performed without limestone addition, so any sulphur capture that occurred was the result of sulphur capture by the ash constituents and by sulphur removal in the recycle gas cooler, which was operated at temperatures below the dew point of water.

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Appendix CanmetENERGY G A Final Phase IV Report … · A Final Phase IV Report Prepared by CanmetENERGY, August 2014 ... the Development of Oxy-fuel Circulating Fluidized Bed Combustion