research and development

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22 Φεβ 2014 (πριν από 3 χρόνια και 3 μήνες)

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Notes on the very
commencement of the
research and development
in the area of noncatalytic
gas
-
solid reaction systems
at the ICPF Prague

Parties involved in the course of time:



M. Hartman, K. Svoboda, O. Trnka, V. Veselý,


M. Pohořelý, M. Čárský, J. Pata, J. Kocurek and others.

Courtesy reminder


Each one of us tends to construct his own biased model of
reality by highlighting some experience (significant) and
neglecting other (irrelevant).

Batch ractor

Plug flow reactor

Mixed flow reactor

Examples of typical noncatalytic
gas
-
solid reactions (NGSR)


Combustion:

C(s) + O2(g)


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-
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,


incineration of solid wastes, calcination, H2S
-
removal, etc., etc.


Elements of the NGSR systems




Mass transfer between single particles and gas stream.



Diffusion of gaseous components through a solid matrix (pores)


and solid state diffusion.



Sorption and chemical reaction.



Heat transfer.



Textural changes brought about by the chemical reaction



and sintering.


Comparison with heterogeneous
catalytic reaction system
s


The most striking difference(s):



-

NGSRs are rather more intricate due to the direct participation



of the solid in the reaction.

-

The texture of the solid changes as the reaction goes on.

-

NGSR systems are inherently transient (of unsteady nature).

-

Analysis involves an additional dimension
-
time.

General reactor behavior /
performance / design



is governed by several
interrelated

quantities
:



-

the flow pattern and contacting gas with solid


-

kinetics: chemical reaction,




transport phenomena,




(heat & mass transfer).

Thermodynamics and mechanical design must also be considered.

Which quantities govern reactor
behavior/performance.

What’s needed to relate output

to input of a reactor.


Reliability of the reactor prediction and design.

The
pragmatic

approach in chemical reaction engineering:


-

abstract from the complexity of the real system and to substitute


a
more or less idealized situation / model

-

that is more amenable to analysis.

The Exxon model fluid cracking unit

Basic types of G
-
S reactors


Six broad types of contactors:


1.
Packed (fixed, static) beds (PB).

2.
Bubbling fluidized beds (BFB).

3.
Turbulent fluidized beds (TFB).

4.
Circulating fluidized beds (CFB).

5.
Moving beds (MB).

6.
Rotating kilns (RK).

Bubbling bed

Big bubble bed

Turbulen
t bed

Slugging

Advantages of FB

-

The rapid mixing of solids leads to near isothermal conditions.

-

The liquidlike flow of particles.

-

Heat and mass transfer rates are high.

Disadvantages of FB


-

Limited understanding of the complex physics of
f
luidization.

-

The erosion, entrainment of fines, bypassing
.


Historical G
-
S systems employed /
explored at ICPF


What for?


As needed steps in the developed new technology of


terephthalic acid (TA).

When?

In the 1960s, early 1970s.



Commercial blast furnace

Disproportionation of potassium
benzoate to terephthalate


(
F. Kaštánek, A. Zemek, J. Kratochvíl, et al.)


400
o
C, 1 MPa

2 C6H5COOK(s)

C6H4(COOK)2(s) + C6H6(g)


Cd, Zn, CO2


m.p. 425
o
C

m.p. > 550
o
C


-

p
erformed in a tub
ular

reactor (MB) with a mixer
,

-

plagued with mechanical problems
,


-

the formation of unwanted humines
,

-

a peculiarity: always starts at the centre of pellets


and spreads outwards
,

-

discontinued.

Sublimation as a means of
refinement of solid with the aid of
the

fluidized bed


(J. (P.) Vítovec, J. Smolík, J. Kugler, A. Haklová, Z. Říha, and others)


-

originated as a wanted operation in the TA process.


The sublimation and thermal decomposition:

C6H4(COONH4)2(s)

C6H4(COOH)2(g) + 2 NH3(g)

350
º
C

N2; H2O

-

has to be accompanied by a condensation / solidification

step


(at 150
o
C)
,

-

the inert bed material: corundum particles (exhibit a high thermal



conductivity)
,


-

a sublimation


condensation pilot plant was designed



and erected
,


-

the excellent outcome of R & D, a number of

foreign



patents granted
,


-

later on, the activities expanded greatly in different


directions
.


-

very efficient
process also
for other materials

(e.g., for phthalanhydride and anthraquinone)
,

The combustion of low
-
grade coal
in the fluidized bed (FBC) with SO2


removal


(
J.Beránek
, V. Havlín, L. Foršt, B. Čech, V. Malaník,


H. Kohoutová, J. Pata, V. Veselý, M. Čárský
,

J. Kocurek,

and many others)

Workplace

In the Department of Chemical Reactors with F. Kaštánek


and J. Čermák as the then Heads.

Period of time

From the early 1970s till the 1980s.

Status and characteristics


-

The application


oriented project.

-

External, strong, influential partners: VŠB Ostrava,


SONP Kladno, strojírny Tlmače.

-

Financing from the State plan of science & engineering


development (SP RVT).

Final aim


The conceptual design,

construction and operation

of

a prototype of the


commercial,
fluidized

boiler

with

desulfurization.

T
1
T
2
T
9
T
10
T
5
T
11
T
8
T
7
T
4
T
2
T
5
T
6
SAMPLING
POINT
600 K
T
3
T
6
T
9
T
10
T
11
T
12
T
12
940 K
1000 K
1135 K
1300 K
1370 K
1230 K
590 K
Fluidized combustor

with SO
2

removal

The attractive features of the FBC


-

The relatively low operating temperature (800


950
o
C).

-

Low
-
value fuels (coals) can be burned.

-

SO2 produced during combustion may be

captured by adding limestone or dolomite into the bed.

Final outcome of the project


-
A smaller commercial / production boiler with all


accessories erected at Trmice (N. Bohemia) and tested.

-

The operational principles found feasible, but the machinery


assessed as overly complicated.

-

Further development discontinued.

NGSR systems important for the
flue and fuel gas cleaning


-

The work commenced as a tiny appendix to the big


„Fluidized combustion with desulfurization“ project (J. Beránek).


-

On a small scale only: with a laboratory or bench
-
scale



apparatus.

Harmful gaseous pollutants of interest


SO
2
(SO
3
), H
2
S, COS, NO
x
.

Solid reactants (sorbents)


CaO, MgO, CaO.MgO, Na
2
CO
3

(active soda).

Precursors
:

-

a host of limestones and dolomites of different



origin from Bohemia & Moravia,

-

(waste) magnesite (Slovakia),

-

hydrated lime (Ca(OH)
2
),

-

calcareous muds,

-

NaHCO
3
.

The conditions of reaction (sorption)


Under ambient pressure, mostly at high temperature: 700


1000
o
C.


In an oxidizing environment (SO
2

from flue gas), in a reducing


one (H
2
S from fuel gas).

Experimental faci
lit
ies developed and employed


-

A high
-
temperature, differential, fixed
-
bed reactor for


the
kinetic studies.

-

A high
-
temperature, fluidized
-
bed, bench
-
scale unit for

the
reactor performance studies
: the batch, continuous,

o
r semi
-
cont. mode of operation.

Crucial problems
: low rate feeding of solids,





heat resistant materials.

-

Cold, transparent (glass) fluidization columns for the




hydrodynamic studies

with different fluidized beds.

Laboratory, fluidized, high

temperature reactor

Pneumatic slide feeder

of solids

Topics / subjects investigated




The thermodynamic constraints on some reactions, e.g.,



sorption of SO
2

by MgO, that of H
2
S / COS by CaO


(the competition with CO
2

in fuel gas).



The changes (often dramatic) in sorbent texture caused



by the „cleaning“ reaction; with the aid of P. Schneider,



D. Tomanová, O. Šolcová et al.; the sintering of
nascent



(fresh sorbent).



The kinetics studies and kin. modeling:


-

the reduction in porosity,


-

intraparticle transport,


-

chemical reaction.



The model equations (PDE) are inherently „
stiff
“ :

Solution of this and other computational problems


developed by O. Trnka (then in the Computing Center).




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History


Thermal decompositions in the fixed and fluidized bed




Hydronium jarosite, H
3
OFe
3
3+
(SO
4
)
2
(OH)
6
; in the elimination


o
f iron from technol. polymetallic solutions.



Dehydratation of sodium carbonate hydrates:



Na
2
CO
3

. 10 H
2
O, Na
2
CO
3

. H
2
O; to produce effective



sorbents, e.g., for NO
x
. A joint project with E. Erdös.



Decomposition kinetics of Ca, Mg
-
hydroxides and the


sintering of the oxides, to achieve high reactivity and special



textural properties of the oxides; with the aid of


O. Šolcová and H. Součková et al.

Combustion of liquid fuels in the fluidized bed




Formation of NO
x

in FBC: the conversion of the fuel
-
bound


nitrogen to NO
2

and NO.



Disposal of waste oils in a rolling
m
ill in Chomutov.

Analysis of the pressure fluctuations within the FB




An efficient means of monitoring the FB behavior,


particularly at elevated temperature.



Started with the participation of J. Drahoš, K. Selucký,



and M. Punčochář.

Higher pressure,

elevated temperature,

fluidized reactor

Acknowledgments

The authors of this expos
é

( M. Hartman and O. Trnka)


wish to appreciate the unflagging attention and interest


shown by the audience.