Note: Descriptions are shown in the official language in which they were submitted.
CA 02774898 2012-03-21
1
METHOD FOR OPERATING A COKE OVEN ARRANGEMENT
The invention pertains to a method for operating a coke oven arrangement,
wherein
the coke oven gas accumulated during the coking process is utilized as a
working
gas.
In practical applications, the coke oven gas accumulating during a coking
process is
usually burned and therefore only utilized energetically although coke oven
gas
contains large amounts of the valuable components hydrogen and methane. The
main reason for reservations against such utilization is that the coke oven
gas is no
longer available as a heating gas and the lacking heating energy needs to be
provided otherwise.
DE 34 244 24 Al discloses a method, in which the coke oven gas accumulating
during a coking process is utilized in the form of a working gas. In this
case,
hydrogen is extracted and a suitable H2-CO ratio is adjusted in order to
subsequently
produce a synthetic natural gas by means of methanation. Since the coke oven
gas
is no longer available for generating the thermal energy required for the
coking
process during this utilization, it is proposed to use blast furnace gas or
methane as
substitute gas for the undergrate firing of the coke oven gas battery. The use
of blast
furnace gas or methane may be considered if a steel mill or a coal mine is
located in
the immediate vicinity of the coke oven plant and the use of these substitute
gases
proves to be economical. Since these requirements only are rarely fulfilled in
practical applications, the coke oven gas usually is only utilized for heating
purposes
as mentioned above.
Other methods for utilizing coke oven gas are known from DE 35 15 250 Al and
DE
38 05 387 Al. In these methods, it is respectively proposed to mix the coke
oven gas
that has a high hydrogen content with blast furnace gas that has a high carbon
monoxide content. The known methods require that blast furnace gas, which
initially
needs to be elaborately cleaned, is available in sufficient quantities.
The present invention is based on the objective of allowing a flexible and
efficient
utilization of the coke oven gas accumulating during the operation of a coke
oven
arrangement.
CA 02774898 2012-03-21
2
This objective is attained with the object of the invention, namely a method
for
operating a coke oven arrangement with the initially described
characteristics,
wherein said method is characterized in that a synthesis gas produced from
fossil
fuel by means of a gasification process is supplied as fuel gas in order to
provide at
least part of the thermal energy required for the coking process. A
particularly high
flexibility of the method for operating a coke oven arrangement is achieved
due to
the utilization of a fossil fuel for producing the synthesis gas. Although
making
available the fossil fuel and carrying out the gasification process for
producing the
synthesis gas is associated with additional investment and process costs,
economical advantages are achieved due to the recovery of the valuable
components contained in the coke oven gas. This applies, in particular, if
coal is
used as fossil fuel because coal is inexpensive in comparison with other
fossil fuels
suitable for carrying out the gasification process, e.g., natural gas, and
already kept
on hand for carrying out the coking process anyway. Consequently, the
inventive
method can be used independently of other production sites such as coal mines
or
blast furnaces. However, if a blast furnace plant is located in the immediate
vicinity, it
is also possible to thermally utilize another portion of the synthesis gas
being
produced in a blast furnace.
According to the invention, it is proposed to extract the gas components such
as
hydrogen and/or methane that accumulate in the coke oven gas during a coking
process and to either utilize these gas components as an end product or to
convert
the gas components into products of even higher value, wherein the lacking
amount
of energy for the coking process and possibly also a blast furnace process is
replaced with the synthesis gas produced from the fossil fuel by means of
gasification. The crude synthesis gas being produced usually only needs to be
desulfurized before it can be utilized as fuel gas in order to provide part of
the
thermal energy required for the coking process, particularly for the
undergrate firing
of coke oven batteries. The synthesis gas used as fuel gas does not require
elaborate processing that, among other things, also includes the removal of
carbon
dioxide.
CA 02774898 2012-03-21
3
According to the invention, the synthesis gas produced from the fossil fuel
may be
exclusively utilized as fuel gas in order to generate thermal energy.
According to one
preferred embodiment of the invention, however, the quantity of synthesis gas
produced exceeds the quantity required as a substitute for the coke oven gas
utilized
in accordance with the invention. It would be possible, for example, to use a
first
portion of the synthesis gas being produced as fuel gas and another portion of
the
synthesis gas being produced for an additional conversion and subsequent
utilization.
In the inventive method, impurities such as tar, naphthalene, aromatic
hydrocarbons
(BTX-components), sulfur and ammonia are initially removed from the coke oven
gas
accumulating during the coking process analogous to a conventional coking
process
known from the state of the art. According to one preferred embodiment of the
invention, the thusly cleaned coke oven gas is compressed in order to extract
hydrogen and/or hydrocarbons. In order to extract hydrogen, it would be
possible, for
example, to carry out a pressure swing adsorption (PSA) in a PSA-system,
wherein
the hydrogen is extracted in highly pure form on the pressure side of the PSA-
system. The pressure swing adsorption may be carried out in a conventional PSA-
system or in a vacuum PSA-system (VPSA-system).
A methane-rich gas is obtained on the expansion side of the PSA-system and
separated from the remaining gas components, particularly carbon monoxide
(CO),
carbon dioxide (CO2), nitrogen, acetylene and residual hydrogen. The removal
of
nitrogen, carbon monoxide and residual hydrogen may be realized, for example,
by
means of a low-temperature distillation, wherein carbon dioxide and water
vapor
previously need to be removed with suitable methods such as, e.g., amine
scrubbing
and/or molecular sieve drying. The hydrocarbon components thusly recovered as
working gas can be supplied to a natural gas network and/or kept on hand for
another synthesis.
CA 02774898 2012-03-21
4
As mentioned above, the gas components recovered from the coking gas can be
used as end products or converted into products of even higher value, wherein
a
portion of the synthesis gas produced during the gasification of the fossil
fuel can
also be used for another synthesis and conversion. Advantageous optional
utilizations are described below.
The extracted hydrogen can be generally utilized as hydrogenating hydrogen in
adjacent chemical plants such as, for example, refineries. According to one
preferred
embodiment, it is proposed to subject the produced hydrogen and a portion of
the
synthesis gas produced due to the gasification of the fossil fuel to an
additional
conversion, wherein the hydrogen is converted into products of higher value
with a
portion of the carbon monoxide of the synthesis gas. It would be possible, for
example, to carry out a synthesis of methanol, as well as the further
production of
fuel by means of an MTG-method (methanol to gasoline), the synthesis of diesel
according to a Fischer-Tropsch method or even the synthesis of ammonia.
If the extracted hydrogen and the synthesis gas that is obtained from the
fossil fuel
and essentially contains carbon monoxide are used for another synthesis, it is
advantageous that a specific hydrogen/carbon monoxide ratio can be freely
adjusted
within a broad range by means of a corresponding inflow control.
In order to additionally increase, in particular, the hydrogen yield of the
entire
method, it would be possible to subject a portion of the produced synthesis
gas to a
CO-conversion. For this purpose, the CO-conversion can be carried out with the
addition of water vapor, wherein carbon dioxide is at least partially removed
after a
desulfurization of the converted synthesis gas, wherein the remaining gas flow
is
subsequently subjected to a pressure swing adsorption in order to remove
hydrogen,
and wherein the off-gas that is depleted of hydrogen and accumulates during
this
process is used as fuel gas for the coking process. This thermally utilized
off-gas
usually represents a portion of the overall fuel gas required for providing
the thermal
energy.
CA 02774898 2012-03-21
The synthesis gas obtained from the fossil fuel may also be utilized for
generating
power with a combined gas and steam turbine plant (GUD-process).
5 According to the invention, a portion of the thermal energy required for the
coking
process is provided by a synthesis gas in the form of fuel gas that is
obtained from a
fossil fuel by means of a gasification process, preferably by means of coal
gasification. The residual gases and waste gases accumulating in the various
subsequent process stages may also be used for burning in order to provide
another
portion of the thermal energy. The off-gas of the preferably used PSA-system,
in
particular, usually still has a high content of combustible components that
can be
thermally utilized by being burned. In addition, high-quality fuels with a
higher
calorific value such as, for example, natural gas can also be admixed. Such an
admixing may be required for adjusting a desired Wobbe index or for
compensating
an energy demand that is not yet covered by the additional fuel gases.
