Note: Descriptions are shown in the official language in which they were submitted.
2184531
-- 1 --
A METHOD FOR PRODUCING HYDROGEN-CARBON
MONOXIDE MIXED GAS, AND APPARATUS THEREOF
The present invention relates to a method for producing
hydrogen (H2)-carbon monoxide (CO) mixed gas, which is used as
a raw material for synthesizing organic compounds, such as
methyl alcohol and/or as fuel for power generation, from coal,
and/or natural gas, and a method for producing methyl alcohol
using the hydrogen-carbon monoxide mixture produced by a
method of the present invention.
A method for producing methyl alcohol using natural gas
as a raw material, and a method using coal as a raw material
are well known to the public.
Regarding using natural gas (main component: CH4), the
method can be roughly divided into two kinds: one uses a
catalyst and the other uses no catalyst. The method using a
catalyst, such as the one disclosed in JP-A-51-29408 (1976),
is mainly used. In accordance with a method using natural
gas, the natural gas is first treated in desulfurizing
equipment for removing hydrogen sulfide (H2S) contained in the
natural gas. Subsequently, the desulfurized natural gas and
steam are introduced into a natural gas reforming equipment
for obtaining H2-CO mixture by a reaction of natural gas and
steam indicated by the following equation (1):
CH4 + H2O ~ 3H2 + CO ... (1)
When a catalyst is used, a nickel-based catalyst
comprising a carrier, such as heat resistant alumina, is used,
and a temperature of 800 ~ 900C is necessary for the reaction
condition. The reaction expressed by equation (1) is an
endothermic reaction, and heat must be supplied continuously
in order to maintain the necessary temperature for the
reaction, i.e. 800 ~ 900C. Generally, the heat of combustion
of natural gas, which is expressed by the following equation
(2), is utilized as a heat source.
2 1 3453 1
- 2 -
CH4 + 2O2 ~ 2H2O + CO2 ... (2)
In the case when a catalyst is not used, a high
temperature in the range of 1000 ~ 1600C is necessary to
produce the reaction expressed by equation (1), and the high
temperature can be obtained by the reaction expressed by
equation (2) in the reactor vessel. In this case, the
reaction expressed by equation (3) also proceeds in the
equipment.
CH4 + CO2 ~ 2H2 + 2CO ... (3)
The generated H2-CO mixture is introduced into methyl
alcohol synthetic equipment for synthesizing methyl alcohol by
the reaction expressed by equation (4).
2H2 + CO ~ CH30H ... (4)
The composition of the H2-CO mixture obtained from natural
gas by the reaction of equation (1) is stoichiometrically
[H2]/[CO] = 3, while the composition of the H2-CO mixture
suitable for synthesizing methyl alcohol by the reaction of
equation (4) is [H2]/[CO] = 2. Therefore, the composition of
the H2-CO mixture must be adjusted in order for the reaction to
proceed effectively. Generally, a shift reaction expressed by
an equilibrium equation (5) is used for converting H2 to CO.
CO + H20 ~ CO2 + H2
Because the reaction proceeds to convert the composition
of the H2-CO mixture obtained from the natural gas from
[H2]/[CO] = 3 to [H2]/[CO] = 2, a part of the H2 must be
converted to CO by adding CO2. One of the general methods for
obtaining CO2 on a commercial scale is pyrolysis of lime stone
(CaCO3). However, the pyrolysis of lime stone is not effective
only for the production of CO2. It is economical only when,
2~84~311 -
- 3
for instance, calcium hydroxide (Ca (OH) 2) iS produced
concurrently.
Accordingly, the shift reaction, wherein CO2 is added, is
seldom utilized in a methyl alcohol production plant, except
when a CO2 production plant is located nearby. Generally, the
excess hydrogen at the methyl alcohol synthesis is separated
with other residual gases from methyl alcohol, and utilized as
fuel for steam heating equipment. That means, the energy of
the excess hydrogen is converted to thermal energy, and
transferred to the energy of steam via a heat exchanger.
Accordingly, a large loss of energy cannot be avoided.
For the reason explained above, the converting efficiency,
which is the rate of energy converted to methyl alcohol from
the natural gas, by the method of producing methyl alcohol
from natural gas, is approximately 70~, and significant
improvement in the converting efficiency cannot be expected
theoretically.
In accordance with a method using coal as a raw material,
coal and an oxidizing agent are introduced into a gasifier for
gasification, as disclosed in U.S. Patent 4,773,917. The gas
generated by the gasification of coal also can be used for
electric power generation, as disclosed in JP-A-59-196391
(1984). Coal itself is an organic compound composed of
oxygen, sulfur, nitrogen, and ashes, in addition to carbon and
hydrogen. However, if it is simplified as CH, the
gasification reaction of coal is essentially expressed by
equation (6).
2CH + 2 ~ 2CO + H2 ... (6)
In order to gasify the coal, the gasification reactor
must be maintained at a temperature in the range of
900 ~ 1600C, but no heat source is necessary, because the
reaction expressed by equation (6) is exothermic. However, if
the exhaust heat is not utilized, the energy utilization
efficiency cannot be improved. The gas exhausted from the
coal gasification reactor contains fly ash and H2S. The fly
2184531
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-- 4
ash is recovered by dust removal equipment, and the H2S is
removed by desulfurization equipment. The composition of H2-CO
mixture gas obtained from coal by the reaction of equation (6)
is stoichiometrically [H2]/[CO] = 0.5. The composition
suitable for synthesizing methyl alcohol from H2-CO mixed gas
is [H2]/[CO] = 2, as expressed by equation (4), and the value
is larger than the ratio of [H2]/[CO] in the H2-CO mixture
obtained by the coal gasification. Therefore, the composition
of the H2-CO mixture obtained by the coal gasification must be
converted in order to produce methyl alcohol. The shift
reaction expressed by equation (5) is used for this
conversion. In this case, a part of the CO is converted to H2
by adding H2O. A temperature drop in the system cannot be
avoided with the addition of H2O, and consequently the addition
of water is a disadvantage for effective utilization of
exhaust heat at the coal gasification. The exhaust heat at
the coal gasification can be recovered as electric power, but
it is impossible to recover it as methyl alcohol.
Theoretically, the exhaust heat at the coal gasification
cannot be reduced to less than about 20~ of the energy of the
coal, nor can the exhaust heat when producing methyl alcohol
from the H2-CO mixture be reduced to less than about 15~ of the
energy of the H2-CO mixture. For the above reason, the ratio
of the energy converted to methyl alcohol to the total energy
of the coal, that is, the conversion ratio is approximately
65~, and a significant improvement to more than 65~ cannot be
expected theoretically.
In accordance with the conventional method of producing
methyl alcohol using natural gas or coal as the raw material,
a significant increase in the efficiency has been
theoretically impossible, even if the most extensive
improvement was obtained for increasing the conversion ratio
to methyl alcohol from the raw material. One of the reasons
is that the composition of the H2-CO mixture suitable for
the production of methyl alcohol must have the ratio of
[H2]/[CO] = 2, while the H2-CO mixture obtained from natural
gas has the ratio of [H2]/[CO] = 3, and the H2-CO mixture
- 21~45~ - 5 -
obtained from coal has the ratio of [H2]/[CO] = 0.5. Another
reason is that the exhaust heat cannot be reduced
theoretically to less than 20~ when coal is used as the raw
material, nor can the exhaust heat be recovered as methyl
alcohol.
One of the objects of the present invention is to provide
a method to produce an H2-CO mixture having an arbitrary ratio
of [H2]/[CO] in the range of 0.5 ~ 3.
Another object of the present invention is to provide a
novel method for producing methyl alcohol using the above
method to produce the H2-CO mixture, which can overcome the
above-mentioned limit of the prior art, and provide a method
for producing methyl alcohol realizing a significantly higher
efficiency and lower cost than the prior art.
Further, another object of the present invention is to
provide an integrated energy system that is capable of using
the above novel method for producing methyl alcohol, and of
responding to variations of power demand in maintaining the
load on the H2-CO mixture production plant stable in concurrent
production of methyl alcohol and electric power.
In accordance with the present invention, an H2-CO mixture
having a suitable composition for producing methyl alcohol can
be produced by using both hydrogen-rich natural gas and
carbon-rich coal as raw materials, and controlling the supply
ratio of the natural gas and the coal. The heat efficiency
can be improved and the need for a heat exchanger can be
avoided by reacting the coal with oxygen, and the natural gas
with steam in the same reactor.
The theoretical background for determining the operating
conditions of the preferred system is explained in detail
hereinafter.
When coal, natural gas, oxygen, and steam are fed into a
reactor simultaneously, a reaction with the coal does not
proceed, because the natural gas, oxygen, and steam are in a
gaseous condition, while only the coal is solid. Comparing
the reactivity of oxygen and steam with natural gas, the
reactivity of the oxygen with the natural gas is larger than
2 1 8453 1
that of steam. Accordingly, a combustion reaction expressed
by equation (8), wherein the natural gas is combined with
oxygen, proceeds prior to the steam reforming the reaction
expressed by equation (7), wherein the natural gas reacts with
steam to generate carbon monoxide.
CH4 + H2O ~ 3H2 + CO ... (7)
CH4 + 2O2 ~ 2H2O + CO2 ... (8)
When the reaction of equation (8) occurs, the generated
H2O and CO2 must be reduced to H2 and CO. Therefore, the
reactions of equations (9) and (10), that is, reactions of H2O
and CO2 with char (carbon component, coal without volatiles can
be used.
C + H20 ~ H2 + CO . . . ( 9 )
C + CO2 ~ 2CO ... (10)
However, the char is utilized and consumed for reducing
the CO2, which is usually contained in volatile coal, and the
H2O and CO2 are generated by the oxidation of H2 and CO, which
are contained in the volatile coal. Therefore, the char
cannot be utilized for reducing H2O and CO2 generated by the
reaction of equation (8).
For this reason when coal and natural gas react in the
same reactor a suitable designing of the reactor and an
adequate setting of the operating condition become necessary,
so that the natural gas does not cause the combustion reaction
of equation (8), but only the steam reforming reaction of
equation (7) proceeds.
First, the reaction with coal is now explained. An
example of coal composition, for instance pacific ocean coal,
is indicated in Table 1.
21 ~4531
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-- 7
TABLE 1
Composition of Coal (Pacific Ocean Coal)
Industrial analysis Wt.
Moisture 2.8
Ashes 14.4
Volatiles 45.2
Fixed Carbon 37.6
Element analysis daf
Carbon 77.82
Hydrogen 6.73
Nitrogen 1.09
Sulfur 0-05
Oxygen 14.32
The reaction of coal with oxygen can be expressed by a
model shown in FIG. 4. In order to indicate the reaction
conditions and others in detail, a molecular formula of coal
is expressed as CaHbOCNdSe, and coal is taken as being composed
of moisture, volatiles, fixed carbon, and ashes in accordance
with the above industrial analysis. The moisture is
evaporated by heating the coal, and the volatiles and char, of
which the main component is carbon, are separated by
pyrolysis. The industrial analysis is performed at
atmospheric pressure, but the reaction proceeds under a
pressurized condition. Therefore, the amount of volatile, V
[~ by weight: wt. ~], generated by the pyrolysis of coal can
be calculated from the value under one atmosphere, V 1 atm
[wt. ~], obtained by the industrial analysis by the following
mathematical equation (1):
V = V 1 atm (1-0.066-ln Pt) (Math. 1)
where,
Pt: Pressure in the reactor [atm]
The pressure in the reactor is preferably set at 30
[atm]. The volatiles react with oxygen to generate CO2 and
21 84~311
-- 8
H2O. This reaction can be expressed by the following equation
(11):
CaHbcNdSe + ~ 2 ~ fC(Char)
+ (b - 2e)/2 H2O + e H2S + d/2 N2
+ (2 (a-f) - c - 2 ~ + (b - 2e)/2) CO
+ (c + 2~ - (b - 2e)/2 - (a - f)) CO2 ... (11)
Steam reforming of natural gas is preferably concurrently
performed in the same reactor by supplying natural gas and
steam. However, the reforming reaction is an endothermic
reaction, and in the case when a large amount of natural gas
is supplied, the heat generated only by the reaction of
equation (11) becomes insufficient. In this case, the supply
amount of oxygen is increased to burn a part of carbon
monoxide as shown by equation (12) to supply additional heat:
2CO + 2 ~ 2C2 ..................................... (12)
The above reactions can be assumed to proceed
instantaneously. The residual char is solid, and the char is
gasified by the reaction with H2O and CO2 which are generated
by the combustion of the volatiles, as indicated by the
following equations (13) and (14):
C (Char) + H2O ~ H2 + CO ... (13)
C (Char) + CO2 ~ 2CO ... (14)
However, these reactions cannot be assumed to proceed
instantaneously, and a part of the char will remain ungasified
if a sufficient residence time is not available. Therefore,
in designing the reactor, the relationship between the carbon
conversion ratio of carbon in the char and the reaction time
must be considered. The relationship between the carbon
conversion ratio, Xchar [-] of carbon in the char and the
reaction time, ~ [s], can be expressed by a model shown by the
following mathematical equations (2), (3), and (4):
2 1 ~453~
-
g
P CharDP 1 -- ( 1 -- Xchar ) + XChar
S PCO + PH o kreact 3kGas
...(Math. 2)
kreaCt = 247exp(- T ) 100
... (Math. 3)
1 T 75
k = 8 725 x 10-5 .
Gas P~DP 2000
... (Math. 4)
Where
PCO2 : Partial pressure of CO2
pH2O : Partial pressure of H2O
Pchar: Density of char
Dp : Particle size of the char
kreaCt: Reaction rate constants of the reactions (13) and (14)
kGaS: Diffusion coefficient
In accordance with the relationship expressed by the
above equations, when oxygen and coal are loaded at a mass
ratio of oxygen/coal of at least 0.8, the residence time of
the coal and the oxygen in the reactor needs to be a few
seconds in order to obtain a gasification ratio of the coal of
at least 0.9. The relationship between the gas generated by
the gasification of coal under the above condition and the
mass ratio of oxygen/coal loaded into the reactor is indicated
in FIG. 5.
As explained above, natural gas and steam are loaded into
the reactor under a condition wherein the reactions of
equations (11), (12), (13), (14) have sufficiently proceeded.
Therefore, the combustion of natural gas expressed by equation
(15) does not occur.
21845~
.
- 10 -
CH4 + 2O2 ~ 2H2O + CO2 ... (15)
Accordingly, an equilibrium of the steam reforming
reaction of natural gas expressed by equation (16) and the
shift reaction expressed by equation (17) must be considered
at the top of the reactor.
CH4 + H2O ~ 3H2 +CO ... (16)
CO + H2O ~ H2 + CO ... (17)
If the partial pressures of the respective gases at the
top of the reactor are expressed as hydrogen p [atm], carbon
dioxide q [atm], steam r [atm], carbon monoxide s [atm], and
methane t [atm], and the equilibrium constant of the steam
reforming reaction of methane of equation (16) is expressed as
K1, and the equilibrium constant of the shift reaction of
equation (17) is expressed as K2, the equilibriums can be
expressed by the following mathematical equations (5) and (6).
p x s = K1
t x r
... (Math. 5)
r x s = K2
p x q
... (Math. 6)
Where, the equilibrium constants at various temperature
are shown in Table 2. The values shown in Table 2 were
calculated by the following mathematical equations (8) ~ (11),
because thermodynamic theory indicates that the equilibrium
constant of a chemical reaction expressed by the mathematical
equation (7) can be calculated by the mathematical equations
(8) ~ (11).
~Vi Ai =
... (Math. 7)
where, Ai : Chemical formula of component I
2184531
vi : A stoichiometric coefficient of the component
I [-] (It is defined as positive for the raw group and
negative for the product group).
TABLE 2
Equilibrium constant
Temperature (K) Kl K2
800 3.07E-02 2.43E-Ol
900 1.27E+00 4.47E-Ol
1000 2.55E+01 7.17E-Ol
10 1100 3.01E+02 1.05E+OO
1200 2.36E+03 1.42E+OO
1300 1.36E+04 1.82E+OO
1400 6.08E+04 2.24E+OO
1500 2.23E+05 2.67E+OO
15 1600 6.94E+05 3.lOE+OO
1700 1.89E+06 3.52E+OO
1800 4.60E+06 3.93E+OO
InK298 = -RT ~ Gfi ... (Math. 8)
(K298) R(To T) (~Vi/~Hfi + ~Lvi - ~I)i Ii(T ))
+ 1 ~ ~i-(Ji(T) - Ji(To)) ... (Math. 9)
Ii~T) = ai-T + 2i T2 + 3i T3 + 4i T4 ... (Math. 10)
2184531
- 12 -
Ji(T) = ai-InT + 2i T + 6i T2 + 12 T3 ... (Math. 11)
Where,
K298 Equilibrium constant [-] at 298.15 [K]
KT Equilibrium constant [-] at a temperature T [K]
To The standard temperature (= 298.15 [K])
T: Temperature [K]
~Gfi: Standard Gibbs energy of formation of a component
i [J/mol]
~Hfi: Standard heat of formation of a component i
[J/mol]
LVi: Heat of vaporization of a component i at To [K]
ai, bi, ci, di: A coefficient of heat capacity at a
constant pressure of a component i
[J/(mol)-Kn)]
The relationship between the oxygen/coal ratio and the
gas concentration at the outlet of the reactor, which is
calculated based on the above equations, is shown in FIG. 6.
In the above calculation, the ratio [mass of natural
gas]/[mass of coal] was taken as 1, and the ratio [mass of
steam]/[mass of natural gas] was taken as 2.
In the above case, the conditions for reacting coal,
natural gas, oxygen, and steam in a reactor to generate an
H2-CO mixture having a ratio [H2]/[CO] equal to 2, and
synthesizing methyl alcohol, are shown in FIG. 7. The loaded
mass ratio of oxygen/coal is taken as 1.2. In accordance with
the above reactions, a reacted gas having a composition of
[H2] = 20%, [H2O] = 15%, [CO] = 43%, [CO2] = 21%, at 1500C can
be obtained. By adding natural gas 1 and steam to the reacted
gas, a reacted gas having a composition of [H2] = 48%,
[H2O] = 19%, [CO] = 24%, [CO2] = 6%, at 1000C can be obtained.
This composition of the gas is suitable for synthesizing
methyl alcohol.
In order to recover the exhaust heat downstream from the
reactor, the mass of steam loaded into the reactor is
2~ 84~3~
- 13 -
preferably small. When making the ratio of [mass of
steam]/[mass of natural gas] = 1.5, a mixture having a
composition of [H2]/[CO] = 2 can be obtained by making the
ratio [mass of natural gas]/[mass of coal] = 1.3, and the
ratio [mass of oxygen]/[mass of coal] = 1.6.
A mixture having a composition of [H2]/[CO] equal to a
value other than 2 can be obtained by selecting the values of
the ratio [mass of natural gas]/[mass of coal] and the ratio
[mass of oxygen]/[mass of coal] from a region shown in FIG. 8,
and adjusting the amount of steam.
Power generating equipment can be installed in parallel
with the methyl alcohol producing equipment at the downstream
region of the H2-CO mixture producing equipment. With the
above system, the rate of operation of the equipment producing
the H2-CO mixture of gases was kept to a constant rate, and the
supply proportion of the H2-CO mixture fed to the methyl
alcohol producing equipment and the power generating equipment
was varied corresponding to the variations in power demand.
Depending on the availability factor of the system, that is,
the rates of operation of the power generating equipment and
the methyl alcohol producing equipment, the most economical
amounts of supplying coal, natural gas, oxygen, and steam were
calculated, and the supply amounts of the raw material were
controlled to be the same as the calculated values.
Practically, the adjustment was performed as follows:
When only methyl alcohol production is performed, the
supply amounts of the raw materials are controlled to obtain a
mixed gas having the ratio [H2]/[CO] = 2, and methyl alcohol is
produced. When both methyl alcohol production and power
generation are performed concurrently, unreacted gas generated
at the methyl alcohol synthesizing equipment is not returned
to the methyl alcohol synthesizing equipment, but is supplied
to the power generating equipment as fuel for power
generation. When only power generation is performed, the
supply of natural gas is stopped, and power is generated using
gas generated from the coal and oxidizing agents.
2184~31
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- 14 -
The composition of the H2-CO mixture for synthesizing
methyl alcohol can be controlled without performing the shift
reaction, and accordingly an effective utilization of energy
can be realized. In a case where the coal and the natural gas
are treated in the same reactor, a heat exchanger to supply
heat for reforming the natural gas becomes unnecessary, and
simultaneously a decrease in the cost for producing methyl
alcohol can be realized by decreasing the number of members
keeping a high energy utilization factor. The efficiency of
producing methyl alcohol can be increased by 10 ~ 15~ in
absolute value from the theoretical limit of conventional
methyl alcohol production by producing methyl alcohol from a
mixed gas having the ratio [H2]/[CO] = 2 generated by a method
of the present invention.
Furthermore, in a system wherein power generating
equipment is installed in parallel with the methyl alcohol
producing equipment, the load for coal gasification can be
kept stable, corresponding to the variations in power demand.
Depending on the availability factor of the system, that
is, the rates of operation of the power generating equipment
and the methyl alcohol producing equipment, the most
economical amounts of supply coal, natural gas, oxygen, and
steam can be calculated, and the supply amounts of the raw
material are controlled to be the same as the calculated
values.
A high efficiency methyl alcohol producing system using
coal and natural gas according to the present invention can
realize a significant energy saving when the energy is
transported by sea for a long distance.
That means, in comparison with the transportation of
solid coal, and the transportation of the natural gas that is
required to liquefy the gas, when the above materials are
converted to methyl alcohol, the handling becomes easy, and
mass transportation by tankers that are used in the
conventional transportation of oil, becomes possible.
2 1 3453 1
- 15 -
In the drawing:
FIG. 1 is a schematic illustration of an integrated
energy system comprising H2-CO mixture producing equipment
using natural gas and coal as raw materials in accordance with
an embodiment of the present invention, methyl alcohol
producing equipment, and power generating equipment;
FIG. 2 is a schematic cross section of an embodiment of a
reactor for realizing the H2-CO mixture using natural gas and
coal as raw materials;
FIG. 3 is a schematic cross section of another embodiment
of a reactor for realizing the H2-CO mixture using natural gas
and coal as raw materials;
FIG. 4 is an illustration for explaining a mechanism of
gasification of coal;
FIG. 5 is a graph indicating the relationship between the
ratio of oxygen/coal loaded into the H2-CO mixture producing
equipment and the gas composition at a lower level of the
reactor;
FIG. 6 is a graph indicating the relationship between the
ratio of oxygen/coal loaded into the H2-CO mixture producing
equipment and the gas composition at an upper level of the
reactor;
FIG. 7 is an illustration indicating optimum operating
conditions of the methyl alcohol producing equipment;
FIG. 8 is a graph indicating the relationship between the
composition of loaded raw material and the composition of H2-CO
mixture;
FIG. 9 is a graph for explaining a method for effectively
operating the integrated energy system that comprises methyl
alcohol producing equipment using natural gas and coal as raw
materials, and power generating equipment;
FIG. 10 is a schematic illustration of a methyl alcohol
producing equipment using a H2-CO mixture, using natural gas
and coal as raw materials; and
FIG. 11 is a schematic cross section of another
embodiment of the present invention.
21 8453 !
- 16 -
(Embodiment 1)
FIG. 1 indicates an integrated energy system in
accordance with an embodiment of the present invention. The
system comprises a raw material supply division 100, a H2-CO
mixture producing division 200, a gas distributing division
500, a methyl alcohol producing division 300, and a power
generation division 400. The raw material supply division 100
supplies coal 10, natural gas 20, oxygen 11, and steam 22 to
the H2-CO mixture producing division 200. The H2-CO mixture is
distributed to the methyl alcohol producing division 300 and
the power generating division 400 by the gas distributing
division 500 in order to supply both methyl alcohol and
electric power.
The structures of the above divisions are now explained
in detail.
The raw material supply division 100 comprises a coal
supply section, an oxygen supply section, a natural gas supply
section, and a steam supply section.
The coal supply section comprises a hopper 110 and a coal
supply control valve 111. The hopper 110 is an apparatus to
store coal pulverized to under-100 mesh 90~, from which coarse
cohesive materials are eliminated, and to pressurize the
atmosphere inside the hopper with nitrogen 12 which is a by-
product from an oxygen producing apparatus 130. The coal
supply control valve 111 controls the amount of the raw coal
supplied, depending on the operating condition of the system.
The oxygen supply section comprises an oxygen producing
apparatus 130 and an oxygen supply control valve 131. The
apparatus 130 is an apparatus to pressurize and liquefy air by
a compressor, and to distill the liquefied air for separating
oxygen and nitrogen, the main component of air. The oxygen
supply control valve 131 controls the amount of the oxygen, an
oxidizing agent, depending on the operating condition of the
system.
The natural gas supply section comprises a natural gas
storage tank 120 and a natural gas supply control valve 121.
The natural gas is supplied directly through a pipe line.
2184~3~
- 17 -
However, the natural gas storage tank is a facility to store
extra natural gas for ensuring stable operation of the methyl
alcohol producing apparatus with a predetermined load, if the
supply of the natural gas through the pipe line becomes
unstable. The natural gas supply control valve 121 is a valve
to control the supplied amount of the natural gas depending on
the operating condition of the system.
The steam supply section comprises a cooling water
storage tank 140 and a steam supply control valve 141. The
liquid cooling water 21 stored in the cooling water storage
tank 140 is heated by being supplied to a heat recovery
portion 213 of a reactor 210 to generate steam 22 at a high
temperature. A part of the steam 22 is supplied to the
reactor 210 through the steam supply control valve 141, which
is a valve to control the supplied amount of the steam
depending on the operating condition of the system.
The H2-CO mixture producing division 200 comprises the
reactor 210, a dust removal apparatus 240, and a desulfurizing
apparatus 2 50.
The reactor 210 comprises a lower stage burner 211 for
supplying the coal 10 and the oxygen 11, an upper stage burner
212 for supplying the natural gas 20 and the steam 22, the
heat recovery portion 213 for cooling the reacted gas, and a
slag cooling tank 221 for collecting slag generated by fusing
the ash components of the coal.
The dust removal apparatus 240 iS an apparatus for
collecting solid dust in the reacted gas, and in practice a
cyclone, or a ceramic filter, can be used.
The desulfurizing apparatus is for removing H2S gas in the
reacted gas, and, for instance, the so-called selexol process
can be utilized. In accordance with the selexol process, H2S
gas is absorbed once into an organic solvent, the absorbed H2S
is extracted from the solution when the concentration of the
H2S in the solution becomes high. The extracted H2S gas having
a high concentration is oxidized to SO2, and the SO2 is removed
by fixing as gypsum by reacting with a slurry of calcium
carbonate, which is a conventional method used in coal fired
21~4~3
- 18 -
power plants. A dry desulfurizaton method can also be used,
wherein H2S gas is directly fixed with fine particles of
calcium carbonate, zinc oxide, or the like.
The methyl alcohol producing division 300 comprises a
5 methyl alcohol synthesizing apparatus 310, a methyl alcohol
distillation section, and heat exchangers. The methyl alcohol
synthesizing apparatus 310 is for synthesizing methyl alcohol
from the H2-CO mixture, and a catalyst, such as a ZnO group
catalyst, can be utilized. The reaction condition is about
300C at 100 atmosphere. The reaction generating methyl
alcohol is an exothermic reaction, and the reaction heat is
recovered and utilized in a rear stage in order to increase
the heat efficiency of the whole system. In order to recover
the reaction heat, heat exchangers 340, 350, 360, are used.
The methyl alcohol distillation section is for obtaining
purified methyl alcohol by removing impurities from crude
methyl alcohol, which comprises a first distillation column
320 and a second distillation column 330. The exhaust heat of
the methyl alcohol synthesizing process recovered by the heat
exchanger 350 can be utilized as the energy necessary for the
distillation.
The power generation division 400 comprises a gas turbine
410, a heat recovery steam generator 420, and a steam turbine
430, which is used for combined cycle power generation.
The gas turbine 410 burns the H2-CO mixture with air 60
pressurized by a compressor, the turbine being driven by the
combustion gas to generate electric power. The heat recovery
steam generator 420 recovers heat energy from the combustion
exhaust gas 65 of the gas turbine 410 in the form of steam 67.
The steam turbine 430 is driven by the steam 67 to generate
electric power.
The operating conditions of the system in the present
embodiment are now explained.
The operation conditions must be determined so that the
coal and natural gas can react in a same reactor. If coal,
natural gas, oxygen, and steam are mixed together and supplied
into the reactor at the same time, the reaction of coal cannot
21~4~3~
- 19 -
proceed, because the natural gas, oxygen, and steam are gases,
but coal is solid. Compared to the reactivity of natural gas
and water with that of natural gas and oxygen, the reactivity
of natural gas and oxygen is high. That means, the combustion
reaction expressed by equation (19), wherein natural gas
combines with oxygen, proceeds first before the steam
reforming reaction expressed by equation (18), wherein the
natural gas combines with steam to generate carbon monoxide,
occurs.
CH4 + H2O ~ 3H2 + CO ................................ (18)
CH~ + 2O2 ~ 2H2O + CO2 ... (19)
Therefore, when making coal and natural gas react in the
same reactor, the operating condition must be controlled so
that the natural gas does not cause the combustion reaction
expressed by equation (19), but proceeds with the steam
reforming reaction expressed by equation (18).
In accordance with the present embodiment of the
invention, the coal and the oxygen are fed into a lower
portion of the reactor, while the natural gas and the steam
are supplied to an upper portion of the reactor. The shapes
of the reactor portions, the methods for supplying raw
materials, and the ratio of supplied coal and oxygen are
controlled so that the coal and the oxygen supplied from the
lower portion into the reactor react sufficiently. If it is
expressed by the ratio of gaseous carbon to total carbon in
the coal, the ratio is at least 0.9, before contacting the
natural gas, and the steam is supplied from the upper portion
into the reactor. Practical compositions and functions of the
reactor are explained in detail in embodiments 2 and 3.
In order to form whirl flows of coal and natural gas in
the reactor, upper burners and lower burners are arranged
oriented in a direction tangential to the inner wall of the
reactor. In accordance with the method explained above, an
H2-CO mixture having a ratio, [H2]/[CO], of 2 was produced, and
methyl alcohol was prepared from the H2-CO mixture.
2~84~33
- 20 -
When methyl alcohol is prepared from the raw materials of
coal (Pacific ocean coal) 100 ton/day, oxygen 120 ton/day,
natural gas 100 ton/day, and steam 200 ton/day, 260 ton/day of
methyl alcohol can be prepared, and the conversion ratio of
energy of the raw materials to the methyl alcohol becomes
about 80~. In comparison with the conventional method for
producing methyl alcohol, a significant increase in the
conversion ratio, such as 10 ~ 15~ in absolute value becomes
possible with this system.
An example of operation of the system is now explained.
Pulverized coal 10 is supplied from a hopper 110 into the
reactor 210 of the H2-CO mixture producing division 200 through
the coal supply control valve 111 and the lower stage burner
211. Oxygen 11 is produced in the oxygen producing apparatus
130 and is supplied to the reactor 210 of the division 200
through the oxygen supply control valve 131 and the lower
stage burner 211.
Pressurized nitrogen 12, which is also obtained at the
oxygen producing apparatus 130 by distillation of liquefied
air, is used for pressurizing the pulverized coal 10. Both
the natural gas 20 stored in the natural gas storage tank 120
of the division 100, and the steam 22 heated by heat recovered
from the reactor 210 by the heat recovery portion 213, are
supplied to the reactor 210 of the division 200 through the
natural gas supply control valve 121 or the steam supply
control valve 141. The reactor 210 shown in FIG. 2 is
provided with the lower stage burner 211 and the upper stage
burner 212 at places separated by a long distance, so that a
certain retention time can be ensured before contacting the
reacted gas of the coal and the oxygen with the natural gas
and the steam. Another reactor shown in FIG. 3, which has a
constriction at a middle portion of the reactor 210, can also
be useful.
Slag, which is fused from coal in the reactor, can be
recovered at a slag cooling tank 221. Exhaust heat from the
reactor is recovered by the heat recovery portion 213 as the
steam 22. The reacted gas 30 from the reactor 210 is treated
2 1 8 ~
- 21 -
by a dust removal apparatus 240 for removing dust, and a
desulfurizing apparatus 250 for removing H2S.
The cleaned H2-CO mixture 40 is distributed by a gas
distributor 500 to the methyl alcohol producing division 300
5 and the power generating division 400.
At the methyl alcohol producing division 300, crude
methyl alcohol 50 is synthesized from the H2-CO mixture 40 by
the methyl alcohol synthesizing apparatus 310. The crude
methyl alcohol is purified by distillation at the first
distillation column 320 and the second distillation column 330
to become purified methyl alcohol 51. At the methyl alcohol
producing division 300, unreacted gas 52 separated from the
crude methyl alcohol at the first distillation column 320 is
heated in the heat exchanger 340, and returned to the methyl
alcohol synthesizing apparatus 310. When electric power is
generated concurrently, the unreacted gas is supplied to the
power generation division 400. Exhaust heat at the methyl
alcohol synthesis is recovered by the heat exchanger 350, and
is utilized at the second distillation column 330 using the
heat exchanger 360.
At the power generation division 400, the H2-CO mixture 40
is burnt with compressed air 60 to drive the gas turbine 410
and generate electric power. Exhaust gas of the gas turbine
410 is recovered by the heat recovery generator 420 as steam
67, and the steam 67 is used for driving the turbine 430.
A method for supplying raw materials to the system is now
explained.
When only methyl alcohol is produced, the H2-CO mixture
gas 40, having a ratio [H2]/[CO] of 2 suitable for producing
methyl alcohol, is produced at the division 200 using coal 10,
an oxidizing agent such as oxygen 11, natural gas 20, and
steam 22. All of the H2-CO mixture is supplied to the methyl
alcohol producing division 300 through the apparatus 500, and
crude methyl alcohol 51 is produced. When only electric power
is generated, the natural gas is not supplied to the reactor,
and the H2-CO mixture 40 is produced at division 200 using
coal 10, which is cheaper than natural gas, an oxidizing
21~4`5~.1
- 22 -
agent, such as oxygen 11, and steam 22. The generated H2-CO
mixture is supplied to the power generation division 400
through the distribution apparatus 500, and power is
generated. In this case, the amount of coal supplied can be
increased by making the upper stage burner changeable from a
natural gas supply to a coal supply, and vice versa. When
both methyl alcohol and electric power are produced, the ratio
of the natural gas 20 supply to the coal 10 supply is
decreased to be smaller than the case when only methyl alcohol
is produced, in order to decrease the cost of the power
generation. In this case, the composition of the H2-CO mixture
40 has a ratio [H2]/[CO] smaller than 2, and unreacted CO gas
52 is generated in the methyl alcohol synthesis. The
unreacted CO gas 52 is separated from the methyl alcohol at
the first distillation column 320, and is supplied to the
power generation division 400 after being heated by the heat
exchanger 340 to be utilized for power generation. Therefore,
the energy utilization efficiency of the whole system does not
decrease. The above relationship is summarized in FIG. 9 as a
graph indicating the relationship of the operating ratio of
the methyl alcohol producing apparatus and the electric power
generation apparatus to the supplied amounts of raw materials
(natural gas/coal, oxygen/coal).
(Embodiment 2)
An embodiment of the reactor 210 of the H2-CO mixture gas
producing apparatus, using natural gas and coal as raw
materials, is indicated in FIG. 2. The whole reactor 210 is
composed of refractory material 216 surrounded by a vessel
217, and the reactor is divided into three zones, an upper
zone 218, an intermediate zone 219, and a lower zone 215.
Upper stage burners 212 are installed in the upper zone, and
lower stage burners 211 are installed in the lower zone. A
slag trap 220 is provided at the lower zone, and a slag
cooling tank 221 is located beneath the slag trap. A
constriction 222 is located at the outlet portion of the
intermediate zone. The upper stage burners 212 and the lower
stage burners 211 are directed in a tangential direction to
~l8~
- 23 -
the inner wall of the reactor so as to form whirl flows as
indicated in FIG. 2. Generally, a plurality of the upper
stage burners and the lower stage burners are provided
circumferentially around the reactor. In FIG. 2, although the
upper stage and the lower stage burners are each shown as only
a single row, they can be arranged in plural rows.
The coal and the oxidizing agent supplied into the
intermediate portion of the reactor from the lower stage
burners form a whirl flow, their reaction being enhanced by
the whirl flow. Similarly, the natural gas and the steam
supplied into the reactor from the upper stage burners form a
whirl flow, their reaction also being enhanced by the whirl
flow.
The function of the present embodiment is now explained.
The coal 10 and the oxidizing agent such as oxygen 11 are
supplied to the reactor from the lower stage burner 211, and
the natural gas 20 and the steam 22 are supplied to the
reactor from the upper stage burner 212. Reacted gas ascends
from the intermediate zone 219 of the reactor to the upper
zone 218, and slag, which is molten ashes of the coal,
descends from the zone 219 to the lower zone 215. The upper
stage burner 212 and the lower stage burner 211 are installed
with an interval between them sufficient for making the coal
10 and the oxygen 11, which are supplied from the lower stage
burner 211, contact the natural gas 20 and the steam, which
are supplied from the upper stage burner, after the coal 10
and the oxygen 11 have reacted sufficiently with each other.
Accordingly, a lower stage reacting zone 223, wherein the
gasification reaction of coal 10 mainly proceeds, is formed at
a lower location inside the reactor, and an upper stage
reacting zone 224, wherein the steam reforming reaction of
natural gas mainly proceeds, is formed at an upper location
inside the reactor. A mass ratio of oxygen/coal supplied from
the lower stage burner 211 is made higher than in the case
when only coal is supplied for the gasification, in order to
ensure a sufficient quantity of heat for steam reforming of
the natural gas 20 supplied from the upper stage burner 212.
2i84~3
- 24 -
The heat energy generated by the gasification of coal in the
reacting zone 223 can be utilized for the steam reforming
reaction of the natural gas in the reacting zone 234 without
using any heat exchanger.
The slag trap 220 allows slag to travel into the slag
cooling tank 221 to be released from the reactor. The slag 31
released from the reactor is cooled in the cooling tank 221
with water to become solid.
The constriction 222 provided at the outlet portion of
intermediate zone 219 of the reactor suppresses release of
unburned char from the zone 219 to outside the reactor. The
suppression of release of the unburned char and the returning
of the char into the zone 219 can prevent a decrease of the
gasification ratio of the coal. Furthermore, the constriction
decreases the downstream release of solids from the reactor
210, and hence the capacity of the dust removal apparatus 240
can be decreased. Particularly, when a ceramic filter is used
as the dust removal apparatus 240, clogging of this filter can
be prevented by providing the constriction. Hence the service
time of the ceramic filter can be extended, so that a decrease
in production costs can be realized.
(Embodiment 3)
Another embodiment of the reactor 210 of the H2-CO mixture
producing apparatus, using natural gas and coal as raw
materials, of the present invention is indicated in FIG. 11.
The whole reactor is composed of refractory material 216
surrounded by the vessel 217, and the reactor is divided into
three zones, such as an upper zone 218, an intermediate zone
219 and a lower zone 215. The upper stage burner 212 is
installed above the lower stage burner 211. An oxygen supply
burner 213 for supplying oxygen is provided between the lower
burner 211 and the upper burner 212. A slag trap 220 is
located at the lower zone, and a slag cooling tank 221 is
located beneath the slag trap. A constriction 222 iS provided
at the outlet of intermediate zone. The upper stage burner
212, the lower stage burner 211, and the oxygen supply burner
213 are directed in a tangential direction to the inner wall
21~4~
- 25 -
of the reactor to form whirl flows. Particularly, the oxygen
supply burner 213 is arranged so that the whirl flow it forms
descends toward the lower part of the reactor. The upper
stage burner 212, the lower stage burner 211, and the oxygen
supply burner 213 are indicated only as a single row in
FIG. 11, but a plurality of these burners can be installed in
plural rows.
The coal 10 and the oxidizing agent such as oxygen 11 are
supplied into the reactor from the lower stage burner 211 to
form a whirl flow, their reaction being enhanced by the whirl
flow. Similarly, the natural gas 20 and the steam 22 are
supplied into the reactor from the upper stage burner 212 to
form a whirl flow, their reaction being enhanced by the whirl
flow.
When a sufficient amount of oxygen, whereby the mass
ratio of oxygen/coal exceeds 1, is supplied to the reactor, if
the whirl flow generated by the lower stage burner is weak,
the temperature in the vicinity of the lower stage burner is
elevated locally by the combustion reaction of the coal.
Therefore, the oxygen, the amount of which exceeds 1 in the
mass ratio of oxygen/coal, is supplied through the oxygen
supplying burner 213, so that the region in which the
combustion reaction of coal occurs readily, is divided into
two zones, respectively in the vicinity of the lower stage
burner, and the vicinity of the oxygen supplying burner. In
accordance with this improvement, local heating of the inside
the reactor to a high temperature can be avoided, so that the
load on the materials that form the reactor can be decreased.
Because the oxygen supplied from the oxygen supplying burner
forms a whirl flow moving toward the lower stage burner, the
oxygen hardly reacts with the natural gas supplied from the
upper stage burner, and the reaction of the natural gas with
the steam is not disturbed. Other functions of the reactor
are the same as the reactor shown in embodiment 2.
(Embodiment 4)
Another embodiment of the reactor 210 of the H2-CO mixture
producing apparatus, using natural gas and coal as raw
218~53~
-
- 26 -
materials, of the present invention is indicated in FIG. 3.
The whole reactor is composed of refractory material 216
surrounded by the vessel 217, and the reactor comprises a coal
gasification chamber 231 and a natural gas reforming chamber
232, which are partitioned by a constriction. The coal
gasification chamber 231 and the natural gas reforming chamber
232 are respectively provided with a lower stage burner 211
and an upper stage burner 212 for supplying raw materials,
which are directed in a tangential direction to the inner wall
of the reactor. A slag trap 220 is provided at the lower
portion of the reactor, and a slag cooling tank 221 is
provided beneath the slag trap. A constriction 222 is
provided at the outlet portion of the reactor. The coal and
the oxidizing agent supplied into the reactor through the
lower stage burner form a whirl flow along the inner wall of
the reactor and descend because of the existence of a central
constriction 230 located at the middle of the reactor, and
turn into an upward stream at the slag trap area.
Accordingly, the retention time of the coal and the oxidizing
agent can be ensured, so that the gasification reaction
proceeds. Similarly, the natural gas and the steam supplied
into the reactor through the upper stage burner form a whirl
flow along the inner wall of the reactor and descends because
of the existence of the constriction 222 and turn into a
straight upward stream at the central constriction 230.
The coal 10 and the oxidizing agent, such as oxygen 11,
are supplied to the reactor from the lower stage burner 211 in
the coal gasification chamber 231, and the natural gas 20 and
the steam 22 are supplied to the reactor from the upper stage
burner 212 in the reforming chamber 232. In this situation,
if it is desired to decrease the size of the reactor,
sufficient distance between the lower stage burner 211 and the
upper stage burner 212 could not be obtained. Therefore, in
accordance with the present embodiment, the central
constriction 230 is provided to effectively separate the
chamber 231 where the coal gasification reaction mainly
2184531
- 27 -
proceeded from the chamber 232 where the natural gas reforming
reaction mainly proceeded.
The mass ratio of oxygen/coal supplied from the lower
stage burner was selected to be higher than the case when only
coal is supplied for gasification, in order to ensure a
sufficient amount of heat for reforming the natural gas
supplied from the upper stage burner. The reactor shown in
the present embodiment can also utilize the heat energy
generated by the coal gasification reaction at the lower stage
reaction area 223 for the steam reforming reaction of the
natural gas proceeding in the upper stage reaction area 224
without using any heat exchanger. It can also use the method
shown in embodiment 3.
The functions of the slag trap 220, the slag cooling
tank 221 and the constriction 222 are as the same as in
embodiment 3.
(Embodiment 5)
FIG. 10 illustrates schematically an embodiment of a
methyl alcohol producing apparatus, using natural gas and coal
as raw materials. The apparatus comprises a coal gasification
reactor 280, a dust removal apparatus 240, a desulfurization
apparatus 250, a natural gas reforming apparatus 260, and a
methyl alcohol synthesizing apparatus 310, which are arranged
in the order listed above.
Raw materials are supplied to the coal gasification
reactor from a coal supply section and an oxygen supply
section. The coal supply section comprises a hopper 110 and a
coal supply control valve 111. The hopper 110 stores coal
pulverized to under-100 mesh 90~, from which coarse cohesive
materials have been eliminated. The atmosphere inside the
hopper is pressurized with nitrogen 12 that is a by-product
from the oxygen producing apparatus 130. The coal supply
control valve 111 controls the supply amount of the raw coal
depending on the operating condition of the system.
The oxygen supply section comprises an oxygen producing
apparatus 130 and an oxygen supply control valve 131. The
oxygen producing apparatus 130 is an apparatus to pressurize
2184~31
- 28 -
and liquefy air by a compressor, and to distill the liquefied
air for separating oxygen and nitrogen, the main component of
air. The oxygen supply control valve 131 controls the supply
amount of the oxygen depending on the operating condition of
the system.
The coal gasification reactor 280 comprises a lower stage
burner 211 and an upper stage burner for supplying the coal
10, and an oxidizing agent such as oxygen 11, and steam 22,
the heat recovery portion 213 for cooling the reacted gas, and
a slag cooling tank 221.
The dust removal apparatus 240 uses a dry process for
collecting solid dust in the reacted gas, in order not to
decrease the temperature of the gas supplied from the coal
gasification reactor to a level lower than 900C, which is a
necessary temperature for producing the steam reforming
reaction of the natural gas in the natural gas reforming
apparatus 260, which is installed in the downstream part of
the reactor. A cyclone or a ceramic filter can be utilized.
The desulfurizing apparatus 250 uses a dry process, the
same as the dust removal apparatus, in order not to decrease
the temperature of the gas. The dry process is a method for
fixing H2S gas directly by a fine powder of calcium carbonate
or zinc oxide.
The methyl alcohol producing division 300 is as the same
as the conventional one.
The steam reforming reaction of the natural gas 20
requires a high temperature of 1600C if no catalyst is used.
In accordance with the method shown in embodiment 1, this high
temperature is obtained by operating the reactor with a high
ratio of oxygen/coal in the coal gasification reactor 280.
However, in this case, the high temperature sometimes exceeds
a suitable temperature for the gasification depending on the
kind of coal. In accordance with the present embodiment, a
catalyst is used in the natural gas reforming apparatus, and
the reforming reaction of the natural gas proceeds at about
9oOC. Accordingly, if a temperature about 1000C can be
obtained by the coal gasification apparatus, it is sufficient
2~845~1
- 29 -
for the reforming reaction of the natural gas. In this case,
although the production cost is high, because respective
reactors for the coal and the natural gas must be provided, a
high efficiency operation in accordance with the nature of the
coal becomes possible. Furthermore, although the coal in the
natural gas are not reacted in the same reactor as in
embodiment 1, the use of a heat exchanger can be made
unnecessary by arranging the coal gasification reactor 280 and
the natural gas reforming apparatus 260 in series, so that
effective utilization of heat as in embodiment 1 becomes
possible.
In accordance with the present embodiment, the conversion
ratio of the raw materials to methyl alcohol is approximately
80~. Accordingly, in comparison with the conventional method,
an improvement of the conversion ratio by 10 ~ 15~ in absolute
value is realized as in embodiment 1.
In embodiments 1 ~ 4, a slurry of coal and water can be
used as the raw material for producing the H2-CO mixture
instead of coal, and a combination of the coal-water slurry,
natural gas, steam, and an oxidizing agent, such as oxygen,
can be used as the raw material for producing the H2-CO
mixture. Using the coal-water slurry instead of coal
facilitates the handling of the raw materials.
