Note: Descriptions are shown in the official language in which they were submitted.
3~2
Carbohydrate Wastes Conversion Process and Apparatus Therefor
This invention relates generally to the conversion of
wastematerials into more useful products, More particularly,
this invention relates to a process for the production of gaseous
and liquid hydrocarbon fuel and chemical products such as methanol
and fertilizer from carbohydrate containing waste materials such
as cereal crop straw, waste wood, garbage and animal manure.
Processes are known for the conversion of such waste
materials into other materials. For instance, it is known to
subject sewage, garbage and the like to a pyrolytic trea~ment to
obtain gases some of which may be used as fuel gases. An example
of a process of this type is described in Canadian Patent 768,558
of Georg Borggreen, issued Oct. 3, 1967. Proposals have also been
made to produce liquid hydrocarbons from carbonaceous materials,
and one such proposal is described in U.S. Patent 3,597,327 of
A.M. Squires, issued August 3, 1971. In Squires' process raw
material such as coal or residual oil islpyrolyzed in the lower
zone of a fluidized bed at a temperature of 900-1700F~ Gaseous
fuel products and coke or liquid~fuels are produced. Another such
process is described by Waterman in Canadian Patent 309,073 dated
March 3, 1931.
In the process described in this patent, carbonaceous
;:~ ' ' .
materials such as coal, cellulose, wood and the like is heated
under pressure with hydrogen or hydrogen-containing gases or with ;
substances yielding h~drogen in the presence of a catalyst com-
prising a mixture of hydrated iron o*ide and hydrated aluminum
oxide. A mixture of liquid hydrocarbons (which appear to be coal
tar products), together with some water, is produced. '
U.S. Patents 3,436t312 and 3,436,314 o Leonor, dated
April 1, 1969, describe a process and apparatus for carbonizing
~e~etable waste materials, such as corn stalks, baga~se and the
like, to orm charcoal. In Lèonor's process, combustible gases
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and condensible vapors from preheating and carbonization stages
are separated into acids, tars and gases which are used as heating
fuel to enable the process to be autothermic, i.e. without re- '
quiring any external supply of heating fuel.
It is also known to convert lignocellulosic material
into various chemical products by a pyrolytic process; one such ~`
process is described by Esterer in U.S. Patent 3,298,928, issued
January 17, 1967, wherein sawdust or wood chips are pyrolytically
converted into levoglucosan and carbohydrate-derived acids by
heating in a gaseous medium at a temperature`of from 600-1500F
for a reaction period of not more than 30 s~conds. `~
Zelnik et al in U.S. Patent 3,660,245, issued May 2, ,-
1972~describe the continuous production of furfural and acetic
acid from lignocellulosic material such as sawdust, and particularly
apparatus for carrying out this process. The lignocellulose
residue is burned to provide heat ~o carry out the reaction.
Alber~tson et al, in Canadian Patent 801,438, issued
December 17, 1968 describe a method of disposing of wet organic
waste material in which the waste matter is fed continuously
into a combustion chamber, in the lower portion of which is a
bed of substantial depth of inert granular material (e.g. sand)
having heat-storing and heat-radiating capability, the material ;
being maintained at a temperature between 1200 and 1800F. A ';
continuous upward stream of air is supplied into the bed through ~ j,
a constriction plate to keep the inert material in a fluidized
state. It is to be noted that Albertson's method and apparatus
are particularly devised so as to ensure that the waste material
is completely combusted; there is no attempt made to recover
products such as gases or fuels from the waste material.
Canadian Patent 809,948 of Miksuru Tada, issued
April 8, 1969 describes a method for continuously burning waste
material containing both combustible and non-combustible material. ~ ~
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The waste material is charged ~nto a furnace having a bed of
a fluidized medium, in which combustion occurs of the combustible
portion of the waste material; the fluidized medium and the non-
combustible portion of the waste are removed from the combustion
zone; separation of the non-combustible portion of the waste
material from the fluidized medium is then effected; the fluidized
medium is recycled to the combustion zone; and the non-combustible
material is discharged. A~ain, there is no teaching or suggestion
of converting the waste material into hydroçarbon fuel products.
In U.S. Patent 3,304,894 of Cox and McMullen, issued
Feb. ~1, 1967, there is described a method for converting refuse
and trash into a uel, in which the waste material is first re- ? ``
duced to a small particle size, after which it is dried, and then ~ -
burned to produce a combustible fuel gas.
The prior art processes mentioned above suffer from
various disadvantages. For instance many known processes are -
inefficient, give low yields of desired products, and/or are
inapplicable to treatment of all carbohydrate-containing waste t
materials, or are unsuitable for producing useful liquid products
such as methanol or liquid hydrocarbons.
The conversion of carbohydrate-containing waste materials
to volatile gases or liquids by partial combustion, using a
limited amount of air or by pyrolysis, involves severe heat
transfer problems and results in a large amount of carbon
dioxide in the product gas.
It is an objective of this invention to provide an
improved process for converting waste carbohydrate-containing
material into useful products such as liquid hydrocarbons suitable
for use as fuels, and alcohols.
A further, more specific objective of the present
invention is a process for the pyrolytic conversion of such
materials as straw, manure, waste vegetation, wood waste and
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garbage into liquid hydrocarbon fuels and/or methanol.
~ nother objective of the present invention is the
provision of a process for converting waste carbohydrate-containing
material as aforesaid, in which all the products obtained from the
process are useful; for example, a process in which, in addition
to the recovery of liquid hydrocarbon fuels and/or alcohols, as
products there are recovered the solid residues of the process
for use either as fuel for process heat or for use as fertilizer.
Still another objective of this invention is the
provision of apparatus, preferably apparatus which is mobile or
portable, ~or carrying out the above process.
We have found that c~lcium carbonate together with
some alkali metal carbonate such as K2CO3 and Na2CO3 can be heated
in a suitable reactor to a temperature sufficient to convert the
calcium carbonate to calcium oxide and further heated to the
desired temperature for use in the conversion process.
At the required temperature it is injected and intimately
mixed with the finely ground carbohydrate-containing feed stock in
a reaction ch~mber. Since the resulting reaction is highly
20 endothermic, the temperature of the media drop rapidly, causing ~`
the carbon dioxide to be absorbed by the CaO, leaving the carbon
monoxide and hydrogen and some combined heavier hydrocarbon com-
pounds which can be converted by catalytic action to useful liquid `
products and then separated by fractional distillation.
The present invention, in one broad embodiment, resides
in a process for the pyrolytic conversion o carbohydrate-
containing waste material to useable products including gaseous
and liquid hydrocarbons and alcohols, which comprises the follow-
ing steps: ;
a) heating a mixture of calcium carbonate and at least
one alkali metal carbonate in a first reaction zone
to a temperature in the range of 1200-1300 whereby ~-~
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calcium carbonate is converted into CaO and CO2;
b) introducing into a second reaction zone a ~ .
feedstock comprising said carbohydrate-containing
waste material in comminuted or pulverized form;
c) simultaneously passing the reaction mixture
resulting from said heating of CaCO3 and alkali
metal carbonate in said first reaction zone to said
second reaction zone, said reaction mixture
comprising a suspension of CaO and alkali metal
~arbonate; and intimately contacting said feedstock :
with said heated mixture therein; thereby effecting
the decomposition of the feedstock into a mixture
of carbon, hydrocarbons and gases including carbon `
monoxide and hydrogen; and at the same time during ~ ; 4
the course of the above reaction said CaO reacts :~
with CO2 therein to form CaCO3; said reactions in ` :`
the second reaction zone occurring at super- . -
atmospheric pressure;
d) separating said gases from the mixture of CaCO3,
alkali metal carbonate and carbon so formed, and ;
withdrawing said gases from the second reaction
zone; :::e) passing the withdrawn gases to a catalytic reactor
wherein are formed said useable products;
f) recycling said suspension of CaCO3, alkali metal - `~
carbonate and carbon to said first reaction zone;
and
g) repeating steps (a) - (f) above.
According to another pre~erred embodiment of the ~ ;
30 invention, a process as described above is carried out, in which
the relative proportions, by weight, of alkali metal carbonate
to CaO are in the range of about 10:1 to about 48:1, there being : ;~
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sufficient alkali metal carbonate to provide a liquid matrix ~or
the CaO, and other solid materials, formed in the reaction occurr-
ing in said second reaction zone, the slurry so formed being
maintained at a temperature of at least 900Co
This invention, in another aspect, resides in a process as
described hereinabove, wherein the reaction mixture comprising
the CaO-containing suspension is in the form of a fluidized
bed in each of said first and second reaction zones, the mixture
being circulated by a flow of gas from the first reaction zone
to the second reaction zone and vice versa.
In still another aspect, this invention resides in an
apparatus for pyrolytically converting carbohydrate-containing
waste material into useable products, which apparatus comprises:
a) rectifier means containing a mixture of aalcium
carbonate and at least one alkali metal carbonate~
said mixture having been heated to a temperature in
the range of 1200-1300C. whereby it is converted to
a suspension of solid material including CaO in a heat
transferring fluid medium, said suspension being
maintained in said rectifier means at said temperature, :
said rectifier means including means for heating the
aforesaid mixture to said temperature of 1200-1300C, ::
and maintaining said suspension at said temperature,
and means for separating gases, including CO2 from said
suspension;
b) means operatively connected to said rectifier means
for the pyrolysis of carbohydrate-containing waste
material in intimate contact with said suspension of
CaO in a fluid medium, and for separation of gases ~ ;
produced by said pyrolysis from said suspension; said
rectifier means (a) and said pyrolysis means (b) being
maintained at superatmospheric pressure;
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c) means for introducing said carbohydrate-containing waste
material feedstock in comminuted or pulverized form
into said pyrolysis means;
d) means associated with said rectifier means and said
pyrolysis means for effecting continuous cycling of said
suspension of solid material in a fluid medium to and
from said rectifier means and said pyrolysis means;
e) means for withdrawing the separated gases from said
rectifier means;
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f) means for withdrawing the separated gases from said
pyrolysis means; and
g) means for converting the separated gases thus withdrawn
from the pyrolysis means into useable products.
In a further aspect, this invention resides in an apparatus
as described above, in which: . -
the rect fier means and said pyrolysis means
comprise two substantially vertically disposed tubular reactors
in a parallel, spaced apart relationship, said reactors being
lined with refractory material, each said reactor assuming the
form of an inverted U, and each of said tubular reactors being
filled to a predetermined level with a suspension of CaO and other ~`
solid materials in a fluid alkali metal carbonate matrix, said
s~spension being maintained at a temperature of at least 900C; the
relative proportions, by weight, of alkali metal carbonate to CaO
being in the range of about 10:1 to about 48
According to a further preferred aspect, the invention re~
sides in an apparatus as described above, in whlch:
said rectifier means and oa d pyrolysis means comprise
20 two substantially vertically disposed tubular reactors, each said
reactor having: (a~ a first substantially straight portion ex-
.
tending substantially vertically at least one-half the vertical `.
height of said reactor; (b) a substantially vertically extending :.
second straight portion substantially parallel to the counterpart
portion of the other reactor, said second straight portion ex-
tending nearly the full vertical height of the reactor; said ' ~`
second straight portion being disposed outwardly of and substan-
tially parallel to, said first straight portion and said second ~ :~
straight portions being also substantially parallel to each otheri :~.
30 and (c) a third substantially straight portion integrally joined .-
to said first straight portion at an obtuse angle,said third `
straight portion and said second stralght portion integrally l:
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merging with a curved portion at the top of the reactor, said
third straight portion being inclined relative to said second
straight portion at an acute angle;
said third straight portions of the rectifier reactor and
the pyrolytic reactor having a spaced-apart, criss-crossing
relationship to each other;
said first mentioned substantially Yertically extending
straight portion of each reactor constituting the main reaction
zone thereof;
the lower end of said second straight portion of each re-
actor integrally merging with a short inwardly extending portion
substantially perpendicular thereto, said inwardly extending por-
tion connecting with the main reaction zone of the opposite re-
actor near the lower end thereof;
each of said reactors being filled to a predetermined level
with a suspension of CaO and other solid materials in a fluid
alkali metal carbonate medium, said medium being maintained at a
temperature of at least 900C.; the relative proportions, by
weight, of alkali metal carbonate to CaO being in the range of
about 10:1 to about 48:1.
In this specification the term "rectify" is used to refer
to the purging of CO2 (and any other wastes that may be removed)
and the consequent conversion by heatin~ of CaCO3 to CaO; and the
term "rectifier" is used to refer to the reactor in which this pro-
cess takes place.
The terms "media" and "medium" ("media" being o course
plural for "medium") are used in the same context and refer to
the alkali metal carbonate - CaO mixture together with the solid
products of the second reaction zone. `~
In the drawings which are attached to and form a part of
this specification:
Fig. 1 is a graph illustrating the decomposition of calcium
carbonate into CaO and CO2 at temperatures in the range of 600-
900 C .;
~: ,
Fig. 2 iS a flowsheet illustrating the process
according to one embodiment of the invention;
Fig. 3 is a flowshee~ illustrating the process accord-
ing to a second and preferred embodiment of this invention;
and
Fig. 4 shows an alternative configuration for ~he
reactor-rectifier used in carrying out the process illustrated
by Fig. 3.
In the process according to the first-mentioned embodi-
ment of the invention, as illustrated by Fig. 2, a dry
granular medium is used, with a preponderance of CaO, with ~-
small amounts of alkali metal carbonate e.g. Na2CO3 and/or
CO3, mixed with it. The mixture is circulated by a flow of
gas from the first to the second reaction zones and vice
versa. In both reaction zones the reaction mixtures are in
the form of fluidized beds.
By the "first reaction zone" we mean the reactor in ~ :
which the calcium carbonate is heated to a temperature
sufficiently high (1200-1300C.) to decompose it into CaO
~0 and CO2 and wherein the Co2 is removed from the system, ie.
the "rectifying" reactor or furnace. By the "second reaction
zone" we mean the reactor in which the carbohydrate-containing
wastes feedstock is admixed and reacted with the hot CaO- ;
conta~ning medium supplied from the rectifying reactor ~or
"first reaction zone") and wherein the feedstock is decomposed
to yield gases comprising hydrogen and carbon monoxide.
Some of the carbon residue from the decomposition of
the carbohydrate-containing wastes feedstock remains in the
.
granular media and is returned with it to the rectifying
3Q furnace where its combustion provides a portion of ~he heat
required for the expulsion of the carbon dioxide as well as
conditioning for the return of the media to the reaction
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chamber. The remainder of the heat required is provided by
burning a portion of the product gas which also assists in
fluidizing the media.
At temperatures above 1000C, the yield is predomin-
an~ly hydrogen and carbon monoxide, which can be synthesized
to straight-chain saturated hydrocarbons or methyl and ethyl
alcoho(~. At lower temperatures the yield consists of a
mixture of heavy hydrocarbon compounds and water which can
be separated by fractional distillation.
This embodiment of the invention will now be described
in more detail with reference to Fig. 2.
Referring to Figure 2, the partially dried raw material -~
is fed to a pulverizer mill 1 which pulverizes the feed stock
to a fine granular meterial. I~ is then fed to a flash drier
2 which dries it to a controlled moisture content ~eg. 26%-27%
moisture by weight of the feedstock~, and heats the material
to a conditioning temperature before it enters the reactor.
The material is then continuously fed to the fluid-bed
pyrolyzer 3~ Simultaneously, the rectifie~ hotll~me~!me~ia and
catalyst is fed from the rectifier furnace 4 at a controlled
rate and temperature and is intimately flash mixed in the
base of the fluid-bed pyrolyzer~ 3. Means (eg. tubes within
which are enclosed oscillating screw feeders) are provided
in both the feed channèls to keep the media and the feed
stock materials closely packed to prevent back flow of the
generated gases from the pyrolyzer. As the mixture rises in
the pyrolyzer the bed is kept fluid by the circulation of a
portion of the product gas by blower 5.
The product synthesis gases and condensible hydro-
carbons are taken off to the heat exchanger 6 and then routed
to fractional distillation columns or-catalytic synthesis
columns depending on the en`d products desired.
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1~393~2
Some of the product fuel is used to supply heat to the
rectifier furnace combustion chamber 7. Waste heat from both
the heat exchanger 6 and the lime rectifier 4 is returned to
the flash drier 2 where it is used for removal of excess
moisture and for temperature-conditioning of the feedstock
material.
In a~sec3nd~and.preferred~d~Y~t o~J~he-invention, the-lfluid-bed
pyrolyzer and rectifier disclosed above is replaced by a -
special-purpose reactor operating at a higher pressure. ~his
reactor is designed to yield products which can be processed
to crude or semi-refined methanol, with by-products of medium
oil and high phosphate fertilizer.
Before proceeding to a detailed description of this
aspect of the invention ~ith reference to Fig. 3, we shall
outline the theory underlying the process, which is believed
to provide a reasonably accurate picture of what occurs in -
said process. We wish to emphasize, however, that we do not
wish to be bound by this theory.
The production of methanol from straw and carbohydrate-
containing wastes is approximately described by the equation,
(I) 2 C12H22~ 8CO + 16H2 + 4C02
The weight relationship is:
90 lb. + 342 lb. -~ 224 lb. + 32 lb. + 176 lb.
Heat balance is~
Q + 2,222,000 btu. - (890,000 + 1,967,000) + 0 = -635,000 btu.
Sensible heat req'd, (as calculated on page 12, hereafter) is:
488,000 btu. Total heat req'd to satisfy equation (I) is: .
635~000 btu. + 488,000 btu. = 1,123,000 btu.
Temperature range is:
70F to 2,300F or 2230F difference. -
The second stage conversion to methanol proceeds
approximately in accordance with the equation~
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(II) 8CO + 16H2 -~CH4O
Weight balance: 224 lb. + 32 ~b. ~ 256 lb.
Heat balance:
890,000 btu. + 1,967,000 btu. - 2,450,000 btu.
= 407,000 btu.
,
Assuming that 60% of the sensible heat can be recovered
for use in the first stage conversion, the net heat that
would
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have to be provided at the expense of the product would be:
1,123,000 ~ ~6 x (407,000 + 488,000) - 587,000 btu.
per mole of straw. This represents a loss of 26.4 ~,
The calculation of sensible heat for straw conversion now
follows.
For CO2, Cp - 12 cal~g-mole C = 11.8 btu./lb-mole F
For H2, Cp = 7.8 cal/g-mole C = 7.7 btu./lb-mole F
For CO, Cp = 22 cal/g-mole C = 6.05 btu./lb-mole F
tl = 70F t2 = 2,300 oF, ` ;
t2 - tl = 2230F
Sensible heat req'd per mole of straw is:
CO 8 x 6.05 x 2230 = 108,000
C2 4 x 11.8 x 2230 = 105,000
H~ 16 x 7.7 x 2230 = 275,000
488,000 btu.
The volume of gas produced at 75 atmospheres and 2300F
pex mole of straw is, to a good approximation for these conditions, ;
359cu ft/lb-mole, so that for
CO: 8 x 359 x ~ x l75 = 199 ~ ft.
~0 C02: 4 x 359 x -g~ x ~-- 100 Cu ft.
~2 16 x 359 x 2760 x 75- 399 Cu f~.
6g8 Cu ~t.
Heat transfer media calculations:
... .. . . . ............... . ~
Considering the heat transfer media to have the specific
heat of Na2CO
= .28 btu per lb. and it must transfer 1,022,000 btu~ the
ratio of the mass of media circulated per lb. of straw is ;~`
-281xl2432o6oo = 19.5 lb., where ~ T - 600F
is the overall temperature difference in the reactor column.
CaO required per lb. of straw for reaction with CO2 is:
~4 x 1376 = .405 lb.: rat1o of Na2CO3:CaO
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= 1905 = ~8.2
Probable minerals trapped in the media per lb. of Ctraw will be:
~ulphur .007 to K2SO4 .039 lb.
Phosphorus .Q25 to NaPO3 .075 lb.
Sodium .007
Potassium .005
Calci~m .007
~agneslum .005
Iron .001
--
TOTAL .057 lb/lb .114 lb.
P = 22
K = 4.38~
It will be seen from Fig. 1 of the drawings that the dis-
sociation pressure of CaCO3 decreases very rapidly as the tempera-
ture drops to 900C or below. Therefore CaO present in the sys~em
will react with most of the CO2 present when the temperature drops
to this value. At 1200C calcium carbonate rapidly dissociates to
CaO and CO2. This is the reason why we employ granular CaO sus-
pended in liquid alkali metal carbonate in our process.
The process according to this aspect of the invention
features the use of molten alkali metal carbonate ( i.e. Na2CO3
and K2CO3) to form a liquid vehicle for a much smaller amount of
CaO in granular form providing a CO2 absorbent. The relative
proportions of Na2CO3, K2CO3 and CaO are not very critical. Suf-
ficient Na2CO3 and X2CO3, however, must be present to provide a
liquid matrix for free circulation, and sufficient CaO must be
present to absorb the excess CO2. The proportion of alkali metal ~ ~`
carbonate, expressed as Na2CO3, to CaO may range from about 10
to about 48:1.K2C03 can be substitute~ for Na2C03 in the same propor-
tions, fluidity being the limiting factor of the lower range.
The liquid alkali metal carbonate components also act as a heat
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transfer medium.
Solids resulting from the pyrolysis of the feedstock i.e.
char, are also suspended in the molten alkali metal carbonate
medium and circulated in the slurry until completely reacted.
Product ash also is suspended in the slurry.
Many other mineral compounds as mentioned previously herein
for instance phosphates and sulphates, will accumulate in both
types of media as end products of the feed stock. Because of this
accumulation, some of the media must be continuously removed and
replaced with new media. That is to say, dry granular media (CaCO3
and alkali metal carbonate) must be periodically fed into the
pyrolysis reactor with the carbohydrate-containing wastes feed-
stock, and an equivalent amount of spent media drained off. The
amount of carbonate added per lb. of feedstock will depend on the
amount of fertilizer produced and on other factors such as viscos-
ity and CaO loss to sulphates and other impurities. However, in
general, fresh make-up carbonate is supplied to the pyrolysis
reactor in an amount of from l to 2 percent by weight, based on the
feedstock. The spent media can be reprocessed or used as~fertilizer
as is or in a refined form depending on market circumstances.
Since the methanol synthesis reaction in accordance
with this process is best carried on at a pressure of 50 to
100 atm. and 400C, considerable saving can be realized by '~
carrying out the reaction wherein the carbohydrate--containing
waste feedstock is decomposed at the same pressure. This
involves compressing the straw feedstock into a solid tubular
mass and extruding it into the reactor. In a particularly
preferred aspect of the invention a combine~. liquid heat transfer
and waste purging medium has been chosen initially to consist
of approximately 48 lb. of Na2CO3 to l lb. CaO. K2CO3 and
other products of the reaction occuring in the second reaction
zone will rapidly mix with th original medium and fresh media
will have to be inte~nittently exchanged. These wastè media
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is a.natural fertilizer and should have market value. Since the
melting point of this medium is 870C, the minimum operating
temperature will be 900C.
These conditions can all be met in the reactor-rectifler
herein described and the reaction in the pyrolysis reactor can be
completely carried out at high pressure.
The invention will now be described in more detail, with
reference to Fig. 3 of the drawings. Referring to Fig. 3, straw
is chopped in chopper 10 to about 1 mm in length, with finer
material intermixed, and is passed into the oscillating screw
feeder 11 which presses it to a dense mass and extrudes the mass
into zone A of the pyîolysis reactor 12.
The reactor-rectifier consists of two inverted U-tubes;
the left tube, 12, with zones A, C, D, and the right zone, 13,
with zones B, F, E. When ready to operate, it is filled with
li~uid media at 900C to the points marked (normal level). The
tubes are lined with refractory material as shown by the dotted
outline. : :
The two U-tubes, 12 and 13, are interconnected by cross
tubes, 14 and 15. The pyrolysis reaction takes place in tube 12, ~.
and rectification takes place in tube 13.
The mixture of CaCO3, Na2CO3 and K2CO3 ~in the required
proportions as.previously indicated) present in tube 13 is heated
to a temperature of 1200-1300C (1250 + 50C). At this tempera-
ture the CaCO3 readily dissociates into CaO and CO2. The CaO gaes
into suspension in molten alkali metal carbonate and this sus-
pension is passed into the pyrolysis reactor 12.
Circulation of the media is up both tubes 12 and 13 and
30 diagonally down the cross tubes 14 and 15. The circulation is :~
driven by gases rising in both tubes 12 and 13 separating above ~.
zones C and F and the dense liquid flowing by gravity down the
cross tubes. The media flowing up tubes 12 and 13 are gas-liquid
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emulsions and the media flowing down cross-tubes 14 and 15 contain
little or no free ~as. The circulation of the media is aided by
the difference in density between the gas-liquid emulsion and the
dense liquid. The media therefore flows approximately in a
figure 8. Gas in U~tube 12 is generated by the thermal break-
down of the extruded straw into synthesis gas and char. The char
remains in suspension in the media and will react with the super-
heated steam the next time around in accor~ance with the water
gas reaction;
H2O + C 3 CO ~ ~I2
alid H20 + CO~ C2 + H2~
It is believed that the alkali metal carbonates act as catalysts
in this reaction. `
Since the stage I reaction is highly endothermic, tempera-
ture of the media drops rapidly between zone A and zone C, and
if properly regulated this drop will be approximately 300C,
bringing the media temperature to about 900C. At this tempera-
ture the CaO suspended in the molten alkali metal carbonate will
react with the CO2 produced by pyrolysis of the carbohydrate-con-
2~ taining waste material feedstock to form CaCO3. The gas isseparàted from the liquid media at zone C. The liquid flows
down tube 14 and also can spill over port 16 and down tube 17. ~ ~ `
~The synthesis gas then escapes up through zone D where any re-
maining media droplets are separated by the U-bend and baffle,
18. `
Because of the endothermic reaction which occurs in reactor
12 it is necessary to supply heat to the system to maintain the
temperature in both tubes 12 and 13 at the desired levels. The ;
temperature is maintained by direct burning of a fuel-air mix-
ture in zone B of U-tube 13 or by hlgh frequency AC current
across the electrode pairs 24 in U-tube 13 and 25 in U-tube 12.
; ~ost of the heat must be supplied in U-tube 13, zone B, in order
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to adequately purge the CO2.
The synthesis gas then travels to heat exhanger 19,
where the gas (comprising a mixture of H2 and CO) is cooled
to about 400C., and thence to condenser 20 and catalytic
reactor 21 where it is formed into methanol, through control
valve 22 and at atmospheric pressure through condenser 23.
Unreacted combustible gas is used to supply process
heat and fuel for prime movers to drive compressors or
electric generators connected with the system (not shown in
the drawings).
The rectifier U-tube 13 is where the most of the heat
is supplied in zones B and F, and if electrically heated, also
across zone A in tube 12. The heat can be provided by a
high frequency AC electric current across the water cooled
electrode pairs 24 and 25,-or it can be supplied by direct
firing (injecting hot-air and gas fuel at 26).
~he hot gas rises with the media from zone B to zone F
raising the media temperature~to 1300C and expelling the CO2.
The separation of the gas from the li~uid phase is exactly
similar to what was previously described for the reactor
U-tube 12. The gas separation may be further encouraged by
use of the apparatus illustrated in ~ig. 4, as further des-
cribed hereinafter.
Gas is expelled through zone E and around baffle 27
and passes into gas turbine 28. The turbinej 28, drives the
turbocompressor, 29, which supplie~ high pressure air to the
base of the reOEtifier, 13, into zone B. The exhaust gas can
alternatively be passed through a heat exchanger and used to
drive a steam turbine for the same purpose or an electric
generator if electric heating is used.
Water is a necessary component of the reaction mixture
in the pyrolytic reactor.
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93~
Normal moisture of the feedstock may at most times be
sufficient to supply the required water,but if not then ext~a
water must be added either with the feed stock or as super-
heated steam. The total water required is in a ratio of
90:342 or 26% by weight of the dry feed stock. Since 5 moles
of water is`needed for each mole of straw, much of the waste
heat can be used to produce super-heated steam which is fed
into the system at point 30 to partially char the straw and
enterzone A for further reaction. As shown in Fig. 3, for ;
this purpose steam at a temperature of 600-800C. and a
pressure of 500-1000 psi. may suitably be used.
The reactor-rectifier is preferably operated at a
pressure in the range of 50-100 atmospheres, and still more
preferably, at a pressure of about 75 atmospheres. ~his is
because the methanol catalytic reactor requires this pressure
for good efficiency.
However, the reactor-rectifier will operate e~ually
well at any pressure down to a few psi above atmospheric
except that its size would have to be lncreased proportion-
ally at lower pressures; and if used for methanol production `~
the synthesis gas would have to be compressed to the required
reacting pressure. This can be done by utilizing the
sensible process heat for steam production and driving a
steam turbo compressor to compress the synthesis gas.
A desirable feature of this invention is to produce ~ ~`
mobile and portable processing apparatus to harvest the
waste materials at their sites and so reduce transportation
costs of raw materials. Since the use of low pressures
would involve larger machinery size and greater weight, it
is definitely preferred to use higher pressures of the order ~
of 5Q-100 atmospheres, as aforesaid. -
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Discussion of Controls:
Operation of the Reactor-Rectifier depends on accurate,
sensitive control.
The pressure in U-tube 13 must be held constant at say
75 atm. or 1125 psi ~ 1 psi. Temperature in zones B and F
must be held constant at 1250C ~ 50C. ~emperature sensing
electrodes, 34 and 35 vary the gas-air mixture entering at 26
by the regulating valves, 36 and 37. Any change in position
of these valves will cause a change in pressure in U-~ube 13.
If the pressure drops, it is sensed by electronic sensor 38
signaling fine-trimming control valve 31 to open wider thus
increasing the pressure drop across gas turbine 28, increasing
its speed and causing the turbo-compresser to ~ncrease its
output thus restoring normal pressure. Excessive pressure
will be corrected in exactly the reverse~manner.
Pressure in U-tube 12 must be nearly equal to the
pressure in U-tube 13; any difference is indicated by a
`difference in level of the fluid media and sensed by level
sensors, 39 and 40. If the level lS low, fine-trimming valve
33 is signalled to restrict gas flow, and if the level is
high, valve 33 opens for less restriction. Valves 22 and 32
are or large adjustments beyond the range of the fine-~ ~`
trimming valves, 31 and 33. If the pressure balance becomes
radically out of balance, say it i5 high in U-tube I2, the
media level is forced down into zone A until the lower open-
ing of tubè 15 is exposed to the gas phase. At this point
nearly all the liquid media will be in U-tube 13 and its
upper surface will be at the high level mark in U-tube 13
sensed by the high level sensor, 40, and the Iow level sensor,
41. Synthesis gas can now escape up cross tube 15 to by pass
tube 42 and exit at 27. Extreme low pressure in U-tube 12
will result in a similar procedure with waste gas travelling
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up cross tube 14 and by-pass tube 17 e~iting at 18. Equilibxium
will be restored b~ correct response'o~ control valves 32 and 22
and fine trimming valves 31 and 33.
Temperature control is accomplished as follows~ The tem-
perature of the liquid media leaving zone F should be 1250C ~
50C, and it should arrive at zone A at the same temperature or
nearly so. If the proper ratio of media to straw feedst`ock
(about 48:l by weight) is maintained, the endothermic xeaction
in zone A will reduce the temperature in the rising column to
900C in zone C. If the temperature difference is less than
this, liquid flow is decreased by temperature senso~rs 43'and 44
signalling fine-trimming valve 33 to increase its restriction -
thus slightly increasing the pressure in U-tube 12'causing `
liguid level to drop slightly in zone C partl~ exposing the'en-
trance of cross tube 14 and reducing the rate of~liquid ~lo~.
This decreases the feed stock to liquid ratio, thus 1ncreasin~
the temperature difference between zone A and zone C. Too high
a temperàture difference will adjust valve 33 for les's restric-
tion causing the liquid level to rise in U-tube 12 to the point
~0 that more of the entrance opening at cross tube 14 is covered
by fluid allowing an increase in fluid flow.
A suitable point for the removal of media i5 shown at
46`in cross tube 15, at which point there is placed a waste`
media port valve. Fluid removed here has travelled at least
through one complete circulation cycle and while s'ome'unreacted
carbonaceous product may be lost, it will be minimal.
Since there is considerable turbulence in the fluid
media due to differential pressure fluctuations and the ~ubbling
of gas rising through the fluid, the top surface boundaries will
only be at the same level momentarily.
For instance, for normal level the fluid should simul-
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~3102
taneously, at some instant, be in contact With level sensors
39 and 49; if not, the liquid volume is too low. Conversely,
if at some instant the liquid is in simultaneous contact with,
for example, level sensors 39 and 40, or 49 and 48, the liquid
volume is too great and port valve 46 will automatically open
~nd drain off sufficient liquid to restore the volume to the
correct amount.
Monitoring of the level sensors by the use of an elec-
tronic logic device including the control of all re ~ ating valves
is imperative.
The choice of valves to be employed in the above- ~ :~
described system may be left to the discretion of the person
sXilled ..
, ~,
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-20a-
93~2
in the art, wishing to practise this process and may be selected
from among those well known types known in the art, and^described -
for instance in the following references:
R.H. Perry and C.H. Chilton, Chemical Enqineers'
Handbook, 5th Edition (1973)
McGraw-Hill Book Co., Section 6, pp. 54-56 and
Section 22, pp. 87-92;
Beard, "Final Control Elements" (1969) Chilton,
Philadelphia Pa.;
Kallen; Handbook of Instrument_tion and Controls
McGraw-Hill Book Co., Section 7, pp. 1-27 and
56-74; and
Crocker and King, Pipinq Handbook, 5th Edition,
McGraw-Hill Book Co. (1967), Sec~ion 7, pp. 61-104.
Referring now to Fig. 4, of the drawings, there is shown
a preferxed configuration for the reactor-rectifier apparatus of
the sys~em illustrated in Fig. 3 and previously described. ~ '
All the functions in this alternative form of the
Reactor-Rectifier are the same as tubes 12 and 13 shown in the
flow sheet of Fig. 3 except that both the reactor tube 12 and the
rectifier tube 13 ha,ve their upper portions zones c-n and F-E
20 sloped at an angle. The angle can be 30 to 75 with 60 preferred.
The reason for the sloping configuration is to facilitate more
rapid gas separation from the liquid phase. As the gas liquid
mixture rises in the sloping portion of the tubes, the gas tends
to float to the upper sloped surface causing a difference in
density between the upper and lower sides oE the tubes. The dense
fluid then flows downward to cross tubes 14 and 15 while the gas ~,
rises to zones E and D.
As will be seen from the foregoing description, for
successful practice o~ the process of this invention several ,'
30 process parameters such as pressure, temperature and the amount of
moisture supplied to the system witp the feed must be scrupulously ~'
controlled. Adequate cooling of the exterior thereof must also
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, .. . - , .. .; ~. .
~L()93~02
be provided. Generally, adequate refractory lining of the
reactor-rectifier will ensure sufficient protection for the metal
exterior, and cooling may be adequately provided by ambient air
motion around the exterior surfaces. If desired, this air motion
may be assisted by properly placed fans (not shown in the drawings).
Cooling of the reactor-rectifier shell could also be effected by
the passage of cooling liquid around its exterior by any suitable
means (not shown in the drawings). The selection and disposition
of circulating fans r or of suitable liquid cooling means about
the reactor-rectifier, is well within the competence of those
skilled in the ar~; and no further discussion of this is deemed
necessary.
The body of the reactor-rectifier may be constructed
of carbon steel or r if necessary or desired, of various alloy
steels. The interior lining may be of magnesite or quartz. Other
materials of construction for the reactor rectifier shell and/or
for the refractory lining could also be used, provided the
materials chosen have the necessary resistance to the temperatures
encountered in the system, and the necessary chemical and corrosion
resistance; generally speaking the selection of appropriate
ma~exials for these purposes can be made by the skilled artisan
from among those known in the art and described, for instance, in
Section 23 of Chemical Engineers' Handbook, 5th Edition (1973)
McGraw-Hill Book Company.
As previously stated the carbohydrate-containing wastes
feedstock is pulverized or comminuted before it is fed to the py
rolytic reactor. The degree to which the feedstock must be pul-
verized is variable to some extent depending on the nature of the
material; but in general it must be pulverized to a degree of fine-
ness that will compress to a sufficiently dense mass so that whenextruded by the oscillating screw feeder, it will effectively pre- ;~
vent back flow of the gas in the reactor. For this purpose,
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~3~2
pulverization to an average particle size in the range of 0.1 to
O.5 mm. will in most cases be adequate.
While the present invention has been described herein in
detail with reference to a preferred embodiment, it is to be ;
understood that the invention is not to be limited thereto. For
instance, the process iæ applicable to carbohydrate-containing
waste materials other than straw, for example, garbage, animal
manure, waste wood, paper, etc. As will be understood by those
skilled in the art, process conditions may be varied to some ,
extent, depending largely on the nature of the end products desired;
and modifications may also be made in the apparatus used without
departing from the aims and scope of the invention. It is desired,
therefore, that this invention be limited only by the claims which
follow.
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~ 23
