Note: Descriptions are shown in the official language in which they were submitted.
20917~8
T 6153
PROCESS FOR PRODUCING A HYDROGEN-CONTAINING GAS
The present invention relates to a non-catalytic process for
producing a hydrogen-containing gas, wherein use is made of direct
heat exchange via high temperature heat storage in refractories.
In particular, the invention relates to a non-catalytic
process for producing a hydrogen-containing gas and/or synthesis
gas from gaseous hydrocarbons such as e.g. methane, natural gas,
associated gas, (i.e. gas produced together with oil in production
fields), naphtha etc. in regenerator-type reactors. In such
reactors which comprise heated solids, alternating combinations of
exothermic and endothermic reactions are carried out in such a
manner that the desired reactions:
CH4 > C + 2H2 and/or
C + H2O - > CO + H2 and/or
CH + H O > CO + 3H
will occur.
However, when using regenerator-type reactors for the
production of hydrogen-containing gases, one is faced with the
problem that the hydrocarbon-containing feed gases have to be
heated to the desired reaction temperature of 1000-1200 C.
However, above a temperature of 400-600 C cracking of the
hydrocarbon-containing feed gases will start leading to the
formation of tarry and sooty material which is interfering with the
desired process conditions through plugging of the equipment
applied.
Thus, it is an object of the invention to provide a process
for production of a hydrogen-containing gas from hydrocarbon-
containing gases using a regenerator-type reactor, wherein the
above problems are avoided.
The invention therefore provides a non-catalytic process for
production of gas essentially comprising hydrogen and/or carbon
monoxide from hydrocarbon-containing gas by contacting the latter
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gas in a regenerator-type reactor with a bed of solids with
endothermic hydrocarbon cracking and/or water gas reaction steps,
by alternating combinations of exothermic and endothermic reactions
vi.a said solids in regenerator-type reactors, characterized in that
the hydrocarbon-containing gas is flash-heated to the desired
reaction temperature of 950-1200 C.
Flash heating is herein defined as a process in which relative
cold gases are heated in a very short time by mixing with very hot
gases.
The invention will now be described by way of example in more
detail by reference to the accompanying drawings, in which: Fig. 1
represents schematically the principle of the invention; and
Figs. 2a, b represent schematically an advantageous application of
the process of the present invention.
Referring now to Fig. 1, a regenerator-type reaction stove 1
is shown, in which stove the endothermic and exothermic reactions
described in the foregoing are carried out.
Regenerator-type stoves as such are known to those skilled in
the art from e.g. blast furnaces and will therefore not be
described in detail.
Generally, it can be said that such a stove is a vessel
comprising a bed of solids which are alternately heated up and
cooled down, dependent on whether exothermic or endothermic
reactions are carried out.
Advantageously the stove is largely filled with a "checker"
work consisting of stacked high temperature resistant refractory
bricks with holes in them through which the gases flow. The stoves
are operated in two cycles. For blast furnaces hot flue gases heat
the checker in downflow. During the heating cycle and during the
cooling cycle the checker in turn heats the upward flow of air for
the blast furnace. During this cycle the stove is operated at the
pressure of 3-S bar. By a proper sequence control the temperature
of the air is held constant at 1290-1320 ~C.
The process according to the invention is suitably carried out
in one or more fixed beds comprising a heated mass of solids. Fixed
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- 3
beds could be applied which may contain heat-resistant solid
material in any desired shape and size, such as a fixed brick
matrix or a packed bed of particulate solids. Particulate solids
such as packed spheres or cylinders with main dimensions ~e.g.
diameter, height of the cylinder) of 1-50 mm, and in particular
2-50 mm, are suitably used in the present process.
Various solid materials may be used in the process according
to the present invention provided that the material is sufficiently
heat-resistant and can withstand large temperature variations which
occur during start-up and shut-down of the process. Suitable solids
comprise refractory oxides, silicium carbide, carbonaceous
materials (e.g. petrol cokes) and mixtures thereof. Metal alloys or
metal compounds may also be suitably used; these materials have the
advantage of possessing a relatively high thermal conductivity and
volumetric heat capacity compared with the previously mentioned
materials. In some cases it may be advantageous to use solids
which, as such or in the form of additional compounds, possess
catalytic activity for at least one of the process steps. However,
in most cases substantlally non-catalytic solids will be most
suited for use in the process according to the invention because
the deposition of carbon on the surface of the solids will usually
lead to a substantial decrease in catalytic activity, if present in
fresh solids. Advantageously, the bed of solids comprises alumina
beads.
Preheating of the solids applied in the process according to
the invention to any temperature suitable for the purpose may be
carried out in various ways. Advantageously, the solids are
preheated to a temperature of 1400-1650 C before being contacted
with the hydrocarbon-containing gas. Suitably the solids are heated
by combustion under pressure of a fuel gas with an oxygen-
containing gas and contacting the combustion gas with the solids,
whereafter the combustion gas is cooled e.g. by preheating the
hydrocarbon-containing gas and/or air.
Various gaseous hydrocarbonaceous materials can be used as
feed for the process according to the invention. In particular
2~91~8
- 4 -
natural gas. methane, associated gas, LPG and evaporated naphtha
ar.e used. In some cases natural gas is preferably subjected to a
treatment to remove sulphur and/or inorganic substances before
using it as feed for the present process.
Via an inlet la at the top of the stove l hydrocarbon-
containing feed gases which usually are preheated from ambient
temperature to 500 C in an indirect heat exchanger (not shown for
reasons of clarity), are introduced into the stove l through any
line 2 suitable for the purpose and an ejector-type compressor 3,
which ensures rapid mixing and is suitable to be applied in a hot
environment. Such compressors are known to those skilled in the art
and will not be described in detail.
The product gas is discharged from the stove 2 via any
suitable outlet lb at the bottom and any line 4 suitable for the
purpose for further suitable processing.
After starting the process by heating the stove in any
suitable manner, the gaseous hydrocarbons are flash-heated through
the disadvantageous temperature zone to a temperature range where
the above desired endothermic reactions occur, by recycling at
least part of the hot product gases through any suitable recycle
line 5 to the feed line 2 and the compressor 3, so that a reaction
mixture comprising feed gases and hot recycled product gas is
supplied to the inlet la.
The following non-limiting Example can be referred to: a
quantity of 214.2 Ton/hr of hydrocarbon-containing feed gas is
supplied to the compressor 3 via the feed line 2 at a temperature
of 500 C and at a pressure of 11 bar.
When recycling, 547.0 Ton/hr of gaseous hydrocarbons are
supplied from the compressor 3 to the inlet la at lO00 C and a
pressure of 7.50 bar, whereas 547.0 Ton/hr of hot product gas at
1281 C and 7.47 bar is discharged from the outlet lb and
subsequently is splitted into 332.8 Ton/hr of recycled gas at
1281 C in line 5 and 214.2 Ton/hr of product gas at 1281 C and
7.47 bar in line 4.
2091748
An additional advantage of the above line up is that the
temperature profile in the stove can be controlled within narrow
ranges. In this way problems as too low cut off temperatures during
the heating of the stove can be avoided.
Figs. 2a and b represent block schemes of an advantageous
embodiment of the invention wherein for heating of the reaction
stove(s) use is made of a flue gas heat recovery stove as used in
e.g. glass ovens. Such heat recovery stove are operating in a
cyclic manner similar to that described earlier with respect to the
blast furnace-type reactor. The process sequence is then as
follows. In Fig. 2a (representing the heating cycle) combustion air
supplied via any suitable line 6 to a heat recovery stove (A) is
preheated in the heat recovery stove (A) to about 1000 C. By
burning some fuel gas such as hydrogen supplied via any suitable
line 2 to the reaction stove 1 with this air a flue gas is formed
with a temperature of 1300 C which is used for heating the
reaction stove 1. After the top heat between e.g. 1000 C and
1300 C has been used for heating the reaction stove 1 the
remaining heat in the flue gas is used to preheat a second heat
recovery stove (B). In the cooling cycle the said heat between
1000 C and 1300 C is then used to accomplish the endothermic
reforming reactions leading to cooling down the stove, after which
the reaction stove 1 is heated again in a heating cycle during
which procedure the combustion air is heated in stove (B) and stove
(A) is heated with the flue gas leaving the reaction stove 1 etc.
(see Fig. 2b).
Reference number 7 represents the flue gas to the stack from
the second preheated heat recovery stove. In Figs. 2a and b the
same reference numerals have been used.
To those skilled in the art it will be clear that in order to
obtain a continuous flow of product gas at least two reaction
stoves are required and at least 2 heat recovery stoves. Proper
sequencing will then result in a more or less continuous flow of
product gas, flue gas and preheated combustion air.
209~748
Various modifications of the present invention will become
apparent to those skilled in the art from the foregoing
description. Such modifications are intended to fall within the
scope of the appended claims.
