(210e) Cold Model Study of Hydro-Dynamic Parameters Affecting the Performance of Re-Circulating Fluidized Bed

Cold
model study of hydro-dynamic parameters affecting the performance of
Re-circulating fluidized bed

Nitin
Lokachari ^a,*,
Sachin Tomar ^a,
Raman Sharma ^b

^a
Department
of chemical engineering - Birla institute of technology and sciences
(BITS), Pilani - 333031, Rajasthan, India.

^b
Senior scientist, CSIR – National environmental engineering
research institute, Delhi zonal centre, New Delhi-110028, India.

^*
E-mail: n.lokachari1@nuigalway.ie
| Tel:
+353-892361399

The
current average global temperature is 0.85 ⁰C
higher than the pre-industrialization period, and ever since is
increasing in an alarming rate. As a result of industrialization,
concentration of CO₂
in
the atmosphere today is 40% higher. The recent Paris climate
conference has set some ambitious targets for the researchers’
world-wide, to limit the global average temperature rise to well
below 2 ⁰C,
which is considered to be the threshold limit before which the
catastrophic effects in the atmosphere are visible. Development of
low carbon technologies are required in-order to meet these
objectives as well as to regulate the increasing CO₂
emissions.

Chemical
Looping Combustion (CLC) is a novel oxy-combustion CO₂
capture technique. In CLC, the fossil fuel combustion is separated
into two parts using metal oxide as the catalyst/ bed material.
Firstly, the metal oxide is oxidized with air in an air reactor (AR),
followed by the reduction of metal oxide using the fuel, in a fuel
reactor (FR).
To
fulfil this criteria of combustion for CLC, some researchers have
tested interconnected reactors arrangement i.e., oxidation and
reduction in two separate reactors and some have used single reactor
which can act as both AR and FR.

In
our study, Re-circulating fluidized bed (RCFB) is proposed to carry
out fuel combustion by adapting CLC technique. RCFB is a spouted
fluidized bed with a central draft tube to induce higher circulation
rates of the bed material. Design and operation of RCFB is simple as
it does not contain cyclone separator and complex loop seal
arrangement which are considered as the main sites for heat loss and
particle attrition.

RCFB
has mainly 4 sections fig 1, starting from the bottom air jet
section, spacer section, draft tube section and free board section.
In the present study, a Perspex made, transparent, concentric and
semi-circular RCFB setup has been fabricated and hydrodynamic
parameters like pressure drop, operating bed voidage, solid
circulation rate and suspension density were studied as they
influence the performance of a RCFB reactor. CLC can be adapted in a
RCFB reactor, where draft tube acts as AR and down-comer as FR.

Fig 1. Schematic representation of cold model RCFB setup at Bits pilani (Pilani campus), India.

For
this study three grades of Indian standard sand has been used as bed
inventory and variables considered are air flow rate, bed inventory,
bed particle size, spacer length between bottom of air jet section
and top of draft tube section. Minimum re-circulating air velocity
has been studied for various operating conditions for the RCFB setup.
An already proposed model for gas bypassing has been used for our
study to analyze the gas bypassing trends for different operating
regimes. Gas bypassing increased with increase in the spacer length
but decreased with bed inventory and particle size. Pressure drop
increases with increase in bed inventory and spacer section. Hence
there is always a trade-off between the parameters with the operating
conditions. Solid circulation rate and suspension density depend on
operating bed voidage and are found to increase with decreasing bed
voidage and with increase in bed inventory and particle size both are
found to increase.

References:

1. Climate science/Greenhouse gasses. Retrieved April 15, 2017, from

http://climatica.org.uk/climate-science-information/greenhouse-gases

2. B. Metz, O. Davidson, H. de Coninck, M. Loos, L. Meyer, Carbon dioxide capture and storage, Cambridge University Press: New York, (2005).

3. T. Mattisson, G.F. Labiano, B. Kronberger, A. Lyngfelt, J. Adánez, H. Hofbauer, Chemical looping combustion using syngas as fuel, International Journal of Greenhouse Gas Control, (2007), 1:158–169.

4. E. Kimball, A. Lambert, A. Fossdal, R. Leenman, E. Comte, W.A.P. van den Bos, R. Blom, Reactor choices for chemical looping combustion (CLC) - Dependencies on materials characteristics, Energy Procedia, 37 (2013), 567–574.

5. M.K. Chandel, B.J. Alappat, Pressure drop and gas bypassing in recirculating fluidized beds, Chemical Engineering Science, 61 (2006), 1489–1499.