Note: Descriptions are shown in the official language in which they were submitted.
: ;
The invention relates to a process for the treatment of coke-
oven gas.
Hot coke-oven gases from a block of coke-ovens are convention-
ally cooled in a succeeding condensing stage. The gaseous as well as the
liquid constituents are further treated in a by-product plant. In this plant
particularly tar, ammonia, sulphur, benzene and naphthalene are removed.
About half of the purified coke-oven gas is reused for undergrate firing of
the block of coke-ovens. In addition blast furnace gas is used for undergrate
firing of the block of coke-ovens. The latter presupposes, that the coking
plant is integrated with a steel making plant in the vicinity of the coking
plant. Because the proceeds that can be realized from the sale of the products
produced in the by-product plant is getting less and less, and because the
economy of production of by-products became doubtful, the production of by-
products has of late been carried out often only for the purpose of gas
purification. Some of the by-products have even been destroyed ~for example,
burning of almmonia).
; It would be a great advantage to use the sensible heat of the
' coke-oven gas, which has a temperature of about 700 to 750C when leaving the
i block of coke-ovens for other processes using heat. This would at the same
time be a lesser load on the environment by heat which no longer has to be
dissipated.
From the journal "Brennstoff-Chemie", Volume 41 (Nr. 10), 1960
.,il
pages 294 to 297 a process is known for producing town gas from natural gas
containing about 90% methane by partial oxidation with oxygen în a free (an
open) flame.
DT-OS 22 32 650 discloses a process for producing a reducing gas.
~ In this process a waste gas from the top of a reduction furnace, for example a
( blast furnace or a shaft furnace is heated with a gas containing methane, for
example coke-oven gas or natural gas is heated. As an example a mixture of
methane or a hydrocarbon gas containing methane, for example cooled and
, . .,. . ;i .;
; : - , ., . :
::. . :
purified coke-oven gas which has subsequently been heated to a temperature
below 1000C, and a gas containing C02~ H20 etc., for example the waste gas
from a blast furnace or shaft furnace which is heated to above 1200C is fed
:into a re:Eorming furnace and the gas is reformed to a reducing gas by heating
to a temperature above 1200C in the reforming furnace. Thus a gas mixture
containing a relative]y high fraction of inert gases, particularly nitrogen,
is produced.
The purpose of the invention is to suggest a process of the
type mentioned at the beginning, in which coke-oven gas is further treated in
an economical way so that at the same time the sensible heat of the coke-oven
gas is utilized and the purification of the coke-oven gas, which is a costly
process, is largely discontinued.
According to the present invention the problem is solved, in
that the hot coke-oven gas coming from the block of coke-ovens is directly,
i.e. without cooling or purification, subjected to partial oxidation by means
of oxygen, oxygen enriched air or other gas mixtures containing oxygen and
cracked and thus converted to a cracked gas rich in carbon monoxide and
hydrogen. ~ ;
In this process the sensible heat transported by the coke-oven
gas is used for the chemical cracking itself ~partial oxidation). During
oxidation most of the impurities in the coke-oven gas are cracked and rendered
harmless so that the costly purification of the coke-oven gas, which was normal
up till now, can be discontinued. At the same time gas for synthesis, gas for
heating or reducing gas with a very high degree of reduction (reducing action)
is formed. Production of by-products is dispensed with, and the high costs of
investment and operation are saved.
A reducing gas with a higher degree of reduction is obtained, if
coke-oven gas is used which is formed by coking of pre-heated coal.
The process can be more economical, if the cracked gas from the
process is used to pre-heat the oxygen or the oxygen enriched air or other gas
mixture containing oxygen.
~lso the heating gas required for coking and/or ~he heating gas
required in a metallurgical plant can be pre-heated by means of the hot
cracked gas.
S:ince the reducing action of the cracked gas is high, it can be
used, particularly in a pit furnace, for direct reduction of iron ore, as is
known from the journal "Stahl and Eisen" 82, Nr. 13 1962, pages 869 to 883.
In a specially conducted process the cracked gas is cooled by
means of a coolant, the cooled cracked gas is compressed, the compressed
cracked gas is finally purified, and the cracked gas thus purified is used,
for example as gas for synthesis, gas for heating or reducing gas, in a pit
furnace. The final stage of purification, which is still required in this
case, is not costly.
Before its further use as gas for synthesis, gas for heating or
reducing gas, the cold finally purified cracked gas may also be economically
pre-heated by means of the hot cracked gas from the process.
It may also be advantageous to compress the hot coke-oven gas
` before the partial oxidation.
The process according to the invention is preferably used for a
; 20 block of coke-ovens which is integrated with a metallurgical plant. In this
case the oxygen plant of the metallurgical plant, which exists anyway and is a ;
large investment, can be used in common and can be fully utili~ed.
Particularly in the latter case waste gas from the pit furnace,
which is available anyway, may advantageously be used for heating of the block ;~
~` of coke-ovens, ~he pre-heating plant for coal or for other heating purposes.
Gasification and treatment of the gas is carried out particular-
` ly in a pressure range from 0 - 30 bar, preferably 0 - 5 bar.
Cracking is preferably carried out at a reaction temperature
from 950 to 1500C.
Purther characteristics, advantages and possibilities of appli-
,
`- ~LC37~
cation of the process according to the invention will be appreciated from the
following description.
The invention may be put into practice in various ways and one
spec:ific embodiment will be described by way of example with reference to the
accompanying drawing which is a diagrammatic illustration of a plant for
carrying out the process according to the invention for the special and
particularly advantageous case of further treatment of hot coke-oven gas which
is produced from pre-heated coal.
The coal which is to be used for coking, is dried in the coal
pre~heating plant 0 and pre-heated to about 200C. The heat-carrying gas,
from which heat is transferred to the coal, is produced in a combustion
chamber by burning the coke-oven gas, blast furnace gas or other fuels. Since
this preliminary stage evaporates and removes water from the coal as well as
heating the coal to about 200C, the time for the succeeding process of coking
can be shortened. Depending on the method chosen for pre-heating, the bulk r
density of the coal in the oven increases to a greater or less extent and that :
improves the quality of the coke. Thus the range of coking coal which is
suitable for coking is widened by means of this pre-heating. More uniform
packing of the coke-oven with pre-heated coal as compared with damp coal, helps
to produce more uniform heating of the packing. As compared with operation
, ~ with damp coal, the coal is converted to coke more uniformly and this in turn
again shortens the time required for coking. For production of reducing gas
from coke-oven gas the combination of pre-heating with the block of coke-ovens
..
1 has a very significant effect on the quality of the reducing gas, as will be
described in more detail below. The coke-oven gas ~a) which is produced in the
block of coke-ovens 1, is fed directly, i.e. without cooling or purification,
to a gasifica~ion plant 2, where the hot unpurified coke-oven gas is partially
oxidized with oxygen, with oxygen enriched air or other gas mix~ures (1)
containing oxygen. For a block of coke-ovens, integrated with a metallurgical
plant, there are no difficulties in using the oxygen from the oxygen plant
~7~
which exists anyway. The cracked gas Cb~, being formed by partial oxidation
in the gasification plant 2, which may be further processed into gases for
synthesis, heating gases or other gases, in the present case particularly into
reducing gases, emerges from gasification plant 2 at about 950 to 1500C. The
hot cracked gas ~b) is cooled in a heat exchanger 3. The heat released is
used for pre-heating of oxygen carrier (1), required for gasification, to
about 200C and for pre-h0ating the purified cracked gas, in the present case
reducing gas (e), to about 800 to 900C. Special cooling is possible as
indicated by the flow of coolant (m) - (n). The wnpurified cold cracked gas
(reducing gas) ~c) is compressed in a succeeding compression stage 4 to about
5 bar. Compression can also take place before gasification, by dotted lines
indicating a compressor between 1 and 2. The unpurified cold and compressed
cracked gas (reducing gas) (d) is then fed through a final purification stage
5. The purified cracked gas (reducing gas) (e) is then pre-heated in heat-
; exchanger 3, as indicated above, and fed to pit furance 6 in the form of pre-
heated cracked gas (reducing gas) (f) and used for direct reduction. The waste -~
gas (h) which is formed in the process of direct reduction in the pit furnace
may be partly used for wldergrate firing of the block of coke-ovens 1, partly
as gas stream (k) as excess gas for other heating purposes in the metallurgical
plant. The so-called waste gas (h) emerging from pit furnace 6 has a heat of
-` combustion of about 2000 to 2500 kcal/m3.
The following comparison shows the special advantage, with
respect to the increased degree of reduction of the cracked gas (reducing gas)
produced, when coke-oven gas from pre-heated coal is used in the process
according to the invention as compared with coke-oven gas ob~ained from damp
coal.
The main point during production of reducing gas is to keep the
fraction of oxidized components in the gas as low as possible or -- expressed
in a different way -- to obtain the highest possible fraction of reducing
components. A measure for the quality oE a reducing gas is its degree of
.
l :;
oxidation
.
C02(m n~ ~ H20(m n) x 100
COz(m n; -~ H20~m n) + H2~m n) ~ CO~m n)
:in which the ratio of oxidized components in the gas to the sum of oxidized
components and reduced components is expressed in %. Generally the process of
direct reduction requires a value of about 5%. Another measure for the quality
of a reducing gas is its degree of reduction
CO~m n) + H2~m n)
CO2~m n) -~ H2O(m n)
which is the ratio of reducing components to oxidized components in the gas.
The following example shows a comparison of production of reducing gas on the
basis of damp and pre-heated coal:
a) using damp b) using
coal pre-heated
coal
1. Characteristics of the
coal used
Volatile components ~% dry) 29.
Ash ~% dry) 9.8
Sulphur % 1.0
Water % 10.0
. m n = normal cubic metre
: a) using damp b) using
coal pre-heated
coal
2. Characteristics and operating
conditions for the block of :~:
coke-ovens and the pre-heating
plant
Width of chamber ~mm) ~50
Bulk density of coking coal 3
in oven ~dry) ~tons/m ) 0.76 0.83
Coking time ~hrs) 18 12.5
Heating flue temperature ~C) 1300 1300
Cont'd.
,~,
~0~Q~:
,
a~ using dampb) using
coal pre-heated
coal
Heat consumption of block
of coke-ovens (kcal/kg
damp coal) 550 360
~leat consumption of pre-
heating plant (kcal/kg
damp coal) - 145
Total heat consumption
(kcal/kg damp coal) 550 505
3. Characteristics of the crude
coke-oven gas produced
:
Temperature ~C) about 700
Pressure (bar abs) about
Gas analysis ~% by volume, dry)
C2 2.0
C0 5.7
H2 59.7
4 25.1
CnHm 3.1
6 6 1.1
H2S 0.7
N2 2.6
Tar ~kg/m3nJ dry gas) 0.13
Phenol (g/m3n, dry gas) 0.7
HCN ~g/m n, dry gas) 0.3
Wa~er content (% in wet gas) about 30 about 3.5
Yield of gas~ dry
(m3n/ton coal, dry) 396 396
Yield of gas, wet
(m3n/ton coal, dry) 565 410
Water content in gas
(m3n/ton coal, dry) 169 14
The insignificant change in gas quality, referred to dry conditions, is neglec-
ted in this comparison because it is unimportant for the product "reducing gas".
: `:
a~ using damp b) using
coal pre-heated
coal
4. Characteristics of the oxygen
a _ ication
Temperature after
pre-heating (C)about 200 about 200
Pressure ~bar) (production) about 5 about 5
_n ysis ~% by volume)
2 99.5
N2/Ar 0.5
Quantity of oxygen
~m3n/ton coal, dry) 91 100
5. Characteristics of the reducing
gas after gasification
Temperature (C) 950 - 1100 1000 - 1150
Pressure (bar) about 0.9
Gas analysis (~0 by volume, wet)
C2 3.20 0.40
C0 20.50 27.90
H2 58.80 60.70
CH4 2.50 2.60
N2 1.30 1.50
H20 13.70 1.90 : :
H2S/COS (g/m n in dry gas) about 5 about 5.2 `
Degree of oxidation
C2 + H20 (m n)
- = 17.8% 2.5%
C2 + H20 + H2 + C0 (m3n)
Degree of reduction
C0 + H2 _(m n)
C2 + H20 (m3n) 4.6 39.8
Quantity of reducing gas
dry (m3n/ton coal, dry) 810 775
Quantity of reducing gas
wet (m n/ton coal dry) 939 790
a) using damp b) using
coal pre-heated
coal
6. Condensation of the reducing gas
To obtain a technically acceptable degree of oxidation or reduction for the
reducing gas which is produced from coke-oven gas, using damp coal, it is
necessary to cool the gas to about 15C in order to remove the water in the gas
by condensation. Using pre-heated coal, this stage of the production may be
mitted.
Temperature ~C) 15
Pressure (bar) about 0.9 about 0.9
Gas analysis (% by volume, wet)
C2 3.6 0.40
C0 23.3 27.90
H2 67.0 60.70
CH4 2.8 2.60
N2 1.5 1.50
H2O 1.8 l.9C
H2S/COS (g/m3n in dry gas)about 5 about 5.2
Degree of oxidation 5.6% 2.5%
Degree of reduction 16.7 35.8
Quantity of reducing gas
dry (m3n/ton coal dry) 810
Quantity of reducing gas
wet (m3n/ton coal) 825
This example for non-pressuri~ed conditions and for various reasons most likely
gasification shows the obvious effect on the ~uality of the reducing gas of
including an upstream stage of pre-heating.
Thus the process according to the invention, using coke-oven
gas produced from pre-heated coal has significant advantages over a process
using coke-oven gas produced fIom damp coal: The throughput of gas is smaller
_ g _
Z
by the amount of water removed by pre-heating; giving a simultaneous improve-
ment in the quality of the reducing gas, the gas throughput of the gasification
plant in all stages including the cooling is reduced by the water content of
the coal; therefore the relevant parts of the plant may be designed to a
small~r scale so that the amount of invested capital is lowered; the fraction
of oxidizing components become less by the absolute amount of water in the
reducing gas; in relation to that the degree of oxidation becomes lower, or the
degree of reduction becomes higher; the lower water content in the hot coke-
oven gas has a corresponding effect during cracking in that it reduces
(equilibrium reaction) the fraction of oxidizing components; the lower water
content in the hot coke-oven gas has the effect of changing the gasification
equilibrium during cracking towards reducing components.
For each isobar there is a minimum for the degree of oxidation
or a maximum for the degree of reduction. The optima are in the range from
0.1 to 7% by volume methane in the dry reducing gas and thus determine the
optimum temperature of reaction for each pressure range. The most economic
pressure range for cracking is from 1 to 5 bar. In this range the lowest
optimum degree of oxidation is obtained for the lowest consumption of oxygen.
- 10 -
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