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Slide 2

Source: José D. Figueroa, National Energy Technology Laboratory (NETL), USDOE

Chemical Looping Technology Improvements through PI

Current project objectives are to:1. What are the efficiencies for CLC technology integrated within

generating facilities

2. Hydrodynamics - Identify gas-solid handling systems to improveintegration of key solids handling

3. To investigate reactor choice used for oxide particles fluidisation

4. Methods for intensifying reduction and oxidation reactions

(Fluidised Beds might not be the best technology to carry out

solid-gas reactions)

Slide 3

Chemical Looping Combustion

Reactions:

- Fuel reactor

(2n + m)MyOx + CnH2m → (2n + m)MyOx−1 + mH2O + nCO2

- Air reactor

MyOx−1 + 1/2 O2(air) → MyOx + (air : N2 + unreacted O2)

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Aspen Plus

Adequate contact time between fuel and air and solid oxygen carrier to achieve

maximum conversion

Size of the two reactors

Adequate solid inventory

Adequate molar flowrate ratio between air and fuel

Issues considered:

Aim:

To develop a fluidised bed model for CLC inspired by a model proposed for FCC

(to replace the Gibbs reactor model, largely used in the literature of CLC)

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Aspen Plus Implementation

The red-ox reaction of NiO/Ni supported by bentonite is investigated.

The fuel reactant is pure methane and the oxidising agent is air.

Within the fuel reactor the specific reduction reaction is:

CH4 + 4NiO CO2 + 2H2O + 4Ni

While within the riser the specific oxidation reaction is:

O2 + 2Ni 2NiO

The un-reacted core model was applied and the controlling step for both oxidation

and reduction reactions is the kinetic step

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Aspen Plus implementationFuel reactor: bubbling regime

Two phase theory: bubble phase with low content of solids and emulsion phase characterised by

perfect mixing of gas and solids

Reactor axially divided into several sections consisting a PFR representing the gas flow through

the bubbles and a CSTR representing the gas flow through the emulsion

Gas mass transfer between bubble and emulsion phase occurs at the exit of the each stages between

the outlet streams

External calculator block in Excel defines the operating conditions of the feed

External calculator and transfer blocks to implement the mass transfer terms

External FORTRAN subroutines used to implement the reactions8

Aspen Plus implementationAir reactor: fast fluidisation regime

Axial distribution of solid particles

Reactor split into a lower and an upper region, the dense and lean phase respectively

One CSTR models the dense phase

Three CSTRs model the upper region characterised by three different mean void fraction

External calculator block in Excel is used to define the operating conditions of the feed

External FORTRAN subroutines are used to implement the reactions

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Results: Bubbling Bed Model

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Results: Bubbling bed model

Conversion increases with the number of stages

The comparison with data from the literature shows that 5 stages give

the conversion observed

Gibbs reactor does not consider gas by-pass in the bubble phase: this

explains the higher conversion

A sensitivity analysis was carried out to find the minimum solid

inventory to achieve more than 90% in methane conversion; this was

found t be 92.5%.

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Results: Riser Model

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Results: Riser model

The set of parameters to achieve a conversion of solid that allows the

circulations of solid particles between air and fuel reactor in steady state

condition was found:

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Uo [m/sec] DR [m] HR [m] Lm [m] Ks [m/sec] Fair/FCH4

1.79 0.8 3.5 0.25 4.41E-04 1.25

Conclusions

The model takes into account hydrodynamics and kinetics

The main process variables can be estimated (e.g. diameter and height of

the two beds, solid inventory, molar flowrate ratios)

The model shows higher accuracy than a Gibbs reactor (it considers the

gas bypass through the bubble phase)

The system can be implemented into the full power plant system to

calculate the process thermal efficiency and attempt economic analysis

and LCA.

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CDF Studies

CFD studies on the Bubbling bed (Fuel) reactor show the issues in creating a workable bed condition

Slide 15

Increasing particle size (decreasing IPF)

2 s

27.2 s 36.8 s

Exp.

Group A/Bdp=125 micron

17.0 s 39.9 s

Group Bdp=350 micron

2 s20.5 s 32.0 s

Group Ddp=800 micron

2 s

Simulation Exp.Exp. Simulation Simulation

Process Intensification

Gas-Solid fluidised beds remain an attractive method for use in chemical and processing industries. However, there are several intrinsic weaknesses and issues including:

Bubbling – bubble formation cause some gas to bypass fluidised particles, resulting in lower gas-solids contact

Elutriation – eventuating in loss of reactants, occasional pollutants (hence need for cyclone). This is exacerbated in larger scale CFB’s operated in turbulent regime to maintain throughput

Scale-up - does not come easily

Large scale - reactor with tall cyclone leads to low mobility and compactness leading towards higher capital and running costs

Umf – the need to match Umf values for the oxidiser and reducer to ensure effective fluidisation and throughput

Slide 16

Future work

Integration of Aspen Plus with CFD modelling to study the gas bypass and the

whole efficiency of the process

• CLC Process Intensification

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