Method for the preparation of a bicarbonate sorbent in flue gas desulfurization

A process for the dry carbonation of an alkali metal or ammonium carbonate, utilizing a low carbon dioxide-containing carbonating gas stream, and more particularly, a process for the production of a bicarbonate sorbent useful in the desulfurization of flue gases from the low carbon dioxide-content flue gases themselves.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the dry carbonation of an alkali 
metal or ammonium carbonate, utilizing a low carbon dioxide-containing 
carbonating gas stream. More particularly, the invention relates to such a 
process for the production of an alkali metal or ammonium bicarbonate 
sorbent useful in the desulfurization of flue gas. 
The conventional technique utilized in the commercial production of sodium 
bicarbonate is the solution process. In the solution process, soda ash is 
dissolved in spent reaction liquor from prior reaction, consisting of 
water and small quantities of dissolved soda ash and sodium bicarbonate. 
The solution is then carbonated to precipitate crystals of sodium 
bicarbonate. The sodium bicarbonate crystals are separated from the liquor 
and dried to yield highly purified, high density crystals. Disadvantages 
of the conventional method are that the procedure requires several steps, 
and necessitates the use of separation equipment, drying of the product, 
and the handling of large volumes of liquids. 
It has also been proposed to make sodium bicarbonate by various dry 
carbonation techniques. In U.S. Pat. Nos. 276,990 Carey et al.) and 
574,089 (Hawliczek), a sodium bicarbonate product is formed by placing 
hydrated soda ash in a revolving cylinder and then introducing carbon 
dioxide into the cylinder. In both patents, reaction times are of the 
order of five to six hours. 
U.S. Pat. No. 3,647,365 (Saeman) teaches a process in which hollow sodium 
bicarbonate beads of low density are prepared in a multistage reactor from 
hydrated soda ash, small amounts of water and carbon dioxide. This process 
requires several steps and must proceed slowly, with carbonation times 
exceeding one hour and drying times up to eight hours. The soda ash must 
first be hydrated in a separate step and the reaction must occur at a 
temperature above 95.7.degree. F. to produce commercially acceptable 
reaction rates. 
More recently, Krieg et al. U.S. Pat. No. 4,459,272, owned by the assignee 
of the present invention, describes a process for the preparation of 
sodium bicarbonate by the reaction of a solid, particulate sodium 
carbonate-containing material with liquid water in a carbon dioxide-rich 
atmosphere. In the Krieg process the particulate mass is mixed in an 
internally agitated or externally rotated or vibrated reactor with the 
water and carbon dioxide. The reaction is carried out at temperatures of 
from 125.degree. F. to 240.degree. F. under atmospheres containing from 
20% to 90% carbon dioxide by volume. The process is carried out under 
reduced water vapor partial pressures to promote evaporation of water from 
the surfaces of the reacting carbonate particles, and to maintain high 
carbon dioxide partial pressures in the reactor atmosphere. Products 
formed by the process have apparent bulk densities as high as 50-60 
lbs./ft..sup.3. 
Each of the previously described dry carbonation techniques is subject to 
particular disadvantages. In each process, the carbon dioxide 
concentration must be high and the reaction temperature must also be high, 
or the reaction rate is prohibitively low. None of these methods can 
produce sodium bicarbonate at low temperatures and low carbon dioxide 
concentrations, at commercially acceptable reaction rates. 
Sodium bicarbonate has also been produced, as well as utilized, in dry 
sorbent injection processes for removing sulfur dioxide emissions from the 
combustion gases of fossil fuel-fired burners. Such techniques have 
commanded considerable attention recently, particularly since they present 
the lowest "first cost" alternative for removing potentially dangerous 
sulfur dioxide from flue gases. Sodium bicarbonate has been demonstrated 
to be a very effective sorbent in the dry sorbent injection process. 
However, the cost of pharmaceutical grade sodium bicarbonate, as currently 
produced, is a major drawback to its use for such purpose. 
U.S. Pat. Nos. 3,846,535 (Fonseca) and 4,385,039 (Lowell et al) disclose 
methods for regenerating sodium bicarbonate from sulfate-containing solid 
waste formed by dry sorbent injection with sodium bicarbonate. The Fonseca 
regeneration step is carried out by forming an aqueous solution of the 
sodium sulfate-containing waste, and treating such solution with ammonium 
bicarbonate to precipitate sodium bicarbonate. The sodium bicarbonate is 
then separated, dried and recycled for further use. Lowell et al discloses 
a regeneration step which involves dissolving the solid desulfurization 
reaction product in a basic liquor, which contains borate ions and/or 
ammonia. Carbonation of this liquor results in a sodium bicarbonate 
precipitate. The Fonseca and Lowell et al processes thus both suffer from 
the use of complicated and capital-intensive solution operations. 
It is among the objects of the present invention to provide an improved 
process for the production of sodium bicarbonate and other alkali metal or 
ammonium bicarbonates, which does not require the multiple operations 
required by prior art solution processes, nor is it limited to use of the 
high temperature, high carbon dioxide-concentration gas mixtures utilized 
in previous dry carbonation techniques. 
A further object of the invention is to provide such a process which may be 
readily employed to produce bicarbonate sorbent employed in the 
desulfurization of flue gases, more efficiently and economically than 
possible utilizing previously proposed techniques. 
These and other objects and advantages of the invention will be described 
more fully below. 
SUMMARY OF THE INVENTION 
In accordance with the present invention a process is provided for the dry 
carbonation of an alkali metal or ammonium carbonate, which comprises 
saturating a gas stream, containing as little as 6% carbon dioxide by 
volume, with water vapor; and fluidizing solid particles of the carbonate 
in the saturated gas stream at a temperature as low as about 85.degree. 
F., the solid particles so mixing with the gas stream that transfer of 
CO.sub.2 from the gas to the surface of the carbonate particles and 
transfer of the heat of reaction from the particle surfaces to the gas 
stream is substantially unhindered. Such efficient mixing is achieved by 
carrying out the carbonation within a turbulent fluidized bed into which 
the fluidizing gas is introduced at a velocity varying from as little as 
about 0.25 to as much as about 15 feet/second, depending upon the size of 
the carbonate particles reacted. 
By so proceeding, carbonation takes place in a thin film on the carbonate 
particle surfaces, and may be carried out at low CO.sub.2 concentrations 
and low reaction temperatures while still achieving commercially 
acceptable reaction rates and conversions. On the other hand, previously 
proposed dry carbonation techniques required the use of high carbon 
dioxide concentrations, and either required high reaction temperatures or 
necessitated lengthy reaction times to provide useful conversions. 
In accordance with a particularly preferred embodiment of the invention, 
the dry carbonation process hereof is utilized in connection with 
desulfurizing low carbon dioxide-content flue gas streams, wherein the 
flue gas is contacted with a solid alkali metal or ammonium 
bicarbonate-containing sorbent to react with sulfur dioxide in the flue 
gas, and the resulting solid waste is separated and removed from the gas 
stream. In accordance with the present invention, the cleansed gas stream, 
from which the solid waste has been removed, is cooled (to a temperature 
as low as about 85.degree. F.), the gas stream is saturated with water 
vapor, and the gas stream is thoroughly mixed with a particlulate alkali 
metal or ammonium carbonate in the manner indicated above. The carbonate 
thus produced is then utilized to contact the hot flue gas for further 
desulfurization thereof. 
Flue gas streams from the combustion of sulfur-containing carbonaceous 
fuels, such as oil, coal, and coke, contain low concentrations of carbon 
dioxide, typically about 8-17% by volume. As illustrated in the following 
table, flue gases also contain amounts of about 3-18% water vapor, 2-4% 
oxygen, 68-77% nitrogen, and up to about 0.5% sulfur dioxide, by volume: 
__________________________________________________________________________ 
COMMON COMBUSTION MATERIALS AND THEIR 
TYPICAL FLUE GAS ANALYSES 
FLUE GAS Sat. 
ULTIMATE ANALYSIS (% BY WT.) 
ANALYSIS (% BY VOL.) 
Temp. 
Fuel S C H N O H.sub.2 O 
Ash 
O.sub.2 
N.sub.2 
CO.sub.2 
SO.sub.2 
H.sub.2 O 
.degree.F. 
__________________________________________________________________________ 
Natural Gas 
0 74.7 
23.3 
0.8 
1.2 
0 0 2.5 
71.3 
8.5 
0 17.7 
136 
#2 oil 0.1 
87.4 
12.5 
0 0 0 0 3 73.6 
11.6 
.005 
11.8 
96 
#6 oil 0.5 
88 11 0 0 0 0.5 
3 73.9 
12.1 
.026 
10.9 
93 
Eastern Coal 
4 57.5 
3.7 
0.9 
5.9 
12 16.0 
3.25 
73.5 
13.8 
.36 
9.1 
88 
Western Coal 
0.48 
47.9 
3.4 
0.6 
10.9 
30.4 
6.4 
3.1 
69.9 
13.6 
.051 
13.4 
126 
Lignite 
0.7 
39.7 
2.9 
0.7 
10.3 
34.9 
10.8 
3.0 
68.2 
13.3 
.09 
15.4 
130 
Coke Breeze 
0.6 
80 0.3 
0.3 
0.5 
7.3 
11.0 
3.4 
76.5 
16.7 
.05 
3.3 
79 
Spruce Bark 
0.1 
51.8 
5.7 
0.2 
38.4 
0 3.8 
3.1 
70.5 
14.8 
.01 
11.6 
96 
__________________________________________________________________________ 
From the preceding, it is apparent that two of the three ingredients 
required to form sodium bicarbonate from soda ash--carbon dioxide and 
water--are already present in flue gas streams. 
Dry carbonation is theoretically feasible under atmospheric pressure, 100% 
relative humidity, in area ABCD of FIG. 1 of the accompanying drawings. 
Prior art disclosures have only described dry carbonation techniques in 
the area GECF. The region covered in presently known processes is so much 
less than the theoretical region in which reaction may be effected because 
commercially acceptable reaction rates and yields could not previously be 
obtained at lower temperatures and carbon dioxide concentrations. For 
instance, below 125.degree. F. the reaction rates in prior art procedures 
are too slow to be of commercial significance, even at very high carbon 
dioxide concentrations. Furthermore, employing such procedures reaction 
rates are too slow to be of commercial significance, regardless of the 
reaction temperature, when carbon dioxide concentrations are below 20% by 
volume. 
In accordance with the process of the present invention, it has been found 
that the region of effective dry carbonation can be expanded to cover the 
additional shaded region HIEGFJ shown in FIG. 1, which permits 
commercially feasible carbonations employing gas mixtures containing as 
little as about 6% by volume carbon dioxide, at carbonation temperatures 
as low as about 85.degree. F. 
Thus, in its preferred form, the present invention provides an efficient 
technique for producing an alkali metal or ammonium bicarbonate-based 
sorbent in the very desulfurizing process in which the sorbent is 
required. The cost of producing, for example, a sodium bicarbonate-based 
sorbent by the present technique is far below that of producing a 
conventional pharmaceutical grade sodium bicarbonate sorbent, since soda 
ash is the only extrinsic raw material required for use in the process. As 
noted above, the other reactants required, carbon dioxide and water, are 
contained in the flue gas and, therefore, do not have to be purchased or 
added to the carbonation reaction in a separate step. The bicarbonate 
product may thus be directly and efficiently produced from flue gas with 
minimum processing. 
Furthermore, the process of the present invention produces a bicarbonate of 
sorbent quality which is uniquely suited for the dry sorbent injection 
process for desulfurizing flue gas, in that its particles are coarse, 
having high surface areas of about 0.4 to 0.55 meter.sup.2 /g., and low 
bulk densities of about 30-40 lbs./ft.sup.3. The use of a high surface 
area, low bulk density sorbent in flue gas desulfurization is desirable, 
since the sorption of sulfur oxides is believed to be surface related. On 
the other hand, commercially produced sodium bicarbonate has a surface 
area of about 0.1 meter.sup.2 /g., and a specific density of about 50-60 
lb/ft.sup.3. 
The particulate carbonate reactant employed in the present process may 
comprise any alkali metal and/or ammonium carbonate-containing material 
such as anhydrous sodium carbonate (soda ash), a sodium carbonate hydrate 
(e.g., sodium carbonate monohydrate), sodium sesquicarbonate, 
Wegscheider's salt, trona (whether or not calcined), the corresponding 
potassium or ammonium carbonates, mixtures thereof, or the like. The 
materials used can be pure or technical grades, or mixtures of carbonates 
with other materials, e.g., sodium chloride. In the following description, 
the process of the invention will be illustrated in connection with the 
preferred carbonation of soda ash. It will, however, be understood that 
the invention is not limited to the use of soda ash, as any of the 
previously mentioned carbonate-containing materials can be employed 
therein.

PREFERRED EMBODIMENTS OF THE INVENTION 
A flow sheet illustrating one embodiment for carrying out the process of 
the invention appears in FIG. 2 of the drawings. As shown therein, a 
carbonating gas stream 10 is introduced into a saturation tank 11, where 
the gas is saturated with water vapor. A portion of the gas stream 10 may 
be diverted from the saturation tank 11 through a proportioning valve 13. 
The gas stream exiting the tank 11 or valve 13 then enters a knockout drum 
14, which removes entrained liquid water from the gas stream. After the 
knockout drum 14, the saturated gas stream enters a fluidized bed reactor 
17, where it is thoroughly mixed with particles of soda ash to produce 
sodium bicarbonate. 
The saturation tank 11 contains water or a salt solution which may be 
maintained at a temperature approximately equal to the desired reaction 
temperature in reactor 17. The gas stream 10 entering the tank is heated 
or cooled to the desired temperature and leaves the tank 11 through line 
12, saturated with water at the temperature of the salt solution in the 
saturation tank. If desired, a portion of the carbonating gas stream 10 is 
passed through the proportioning valve 13, by-passing saturation tank 11 
and being re-mixed with saturated gas stream 12 after the latter exits 
from the saturation tank. In this manner, both the temperature and 
moisture content of the carbonating gas stream is precisely regulated. 
Gas stream 15 is thereafter fed into a knockout drum 14, which removes 
entrained liquid water and minimizes any fouling of a gas distribution 
plate 16 in the fluidized bed reactor 17 downstream thereof. 
The gas stream 18 removed from the knockout drum is mixed in the fluidized 
bed of reactor 17 with a particulate soda ash feed 19 and, optionally, 
with liquid water which may be sparged into the bed through line 20. The 
soda ash may be added batchwise, or continuously, at a rate proportional 
to the conversion to bicarbonate. The liquid water may be added to control 
the rate of reaction or the reaction temperature by providing evaporative 
heat removal. In many cases no liquid water need be added at all. The 
deliquescent properties of some of the carbonate reactants is sufficient 
to remove enough water from the saturated carbonating gas to allow the 
reaction to proceed without the further addition of liquid water. 
As indicated hereinabove, to effect thorough mixing of gas stream 18 and 
particulate soda ash feed 19 it is critical to carry out the carbonation 
in a turbulent fluidized bed under conditions which produce thorough 
contact between the solid and gaseous reactants with substantially 
complete back mixing and heat transfer therebetween. Such conditions are 
insured by introducing the fluidizing gas into the fluidized bed at rates 
varying from about 0.25 to 15, preferably about 0.5 to 10, feet/second. In 
particular, employing fine soda ash particles (e.g., particles of the 
order of 2 microns) the carbonating gas stream may be introduced into the 
fluidized bed at rates as low as 0.25 ft./sec. and still produce turbulent 
flow conditions therein. On the other hand, when coarse soda ash particles 
are reacted (e.g., particles of the order of 200 microns), it may be 
necessary to introduce the carbonating gas at velocities of up to 10 
ft./sec., or even as much as 15 ft./sec., to effect fluidization. 
These conditions may be provided in either a conventional gas fluidized bed 
reactor in which the energy required to fluidize the soda ash particles is 
imparted to the carbonating-gas stream, or in a mechanically fluidized bed 
wherein the solid particles are mechanically accelerated through the 
gaseous medium to effect turbulent fluidization thereof. In a mechanically 
fluidized bed the flow rate of the carbonating-gas stream must at least be 
equal to that necessary to supply the gaseous reactants and to remove the 
heat of reaction. In a gas fluidized bed the gas feed rate must also be 
sufficient to produce turbulent fluidization; in most instances, such feed 
rate is significantly greater than that required for adequate feed of the 
reactants and heat removal. Employing such conditions commercially 
acceptable carbonation rates are obtained, employing gas streams 
containing as little as about 6-17% CO.sup.2 by volume, at temperatures as 
low as about 85.degree. F. and up to about 200.degree. F., preferably 
about 100.degree.-190.degree. F. 
In accordance with another important feature of the invention, the 
carbonating-gas stream in reactor 17 is maintained under substantially 
saturated conditions, i.e., the moisture content in the fluidized bed is 
maintained at at least about 90% of saturation at the reaction temperature 
utilized, either by feeding carbonating gas stream 10 solely through 
saturation tank 11 or by additionally vaporizing some liquid water sprayed 
into the reactor. As long as a minimum of 90% relative humidity is 
maintained in the fluidized bed, more water is adsorbed onto the surfaces 
of the reacting soda ash particles than is evaporated therefrom. In this 
manner, the presence of sufficient water on the surfaces of the reacting 
particles is assured, and the carbonation reaction proceeds at 
commercially acceptable rates. 
Following carbonation in reactor 17 the bicarbonate product is discharged 
from line 21, and the unreacted gas is continuously removed overhead 
through vent 22. 
It should be understood that the unit operations depicted in FIG. 2 may 
vary widely without departing from the scope of thls invention. For 
instance, the saturation tank 11 may be replaced by an externally cooled 
or heated heat exchanger followed by a water spray for saturating the 
carbonating gas stream. Similarly, the knockout drum 14 may be a demister 
pad or may be dispensed with if not required by the particular design of 
the fluidized bed reactor 17 employed. 
A preferred embodiment of the carbonation process hereof resides in the 
desulfurization of flue gases by the dry injection technique. The 
invention makes possible the direct use of low carbon dioxide-content flue 
gas containing about 8-17%, typically about 10-13%, CO.sub.2 by volume. 
For example, as illustrated in FIG. 3, in one preferred embodiment a 
boiler flue gas stream 30 containing fly ash and sulfur dioxide, is 
recovered from a boiler at approximately 300.degree. F. As indicated 
above, such a stream may typically incorporate about 8 to 17% carbon 
dioxide, 2-4% oxygen, 68-77% nitrogen, 3-18% water vapor, and up to 0.5% 
sulfur dioxide, by volume. The flue gas is mixed with a sodium 
bicarbonate-based sorbent which may also contain, for example, sodium 
carbonate and sodium sulfate, metered from a storage bin 31 into the flue 
gas stream via line 32, the sorbent reacting with the sulfur dioxide in a 
particulate collection device (PCD) 33. 
Solid wastes 34 are discharged from the PCD 33 and a clean flue gas stream 
35 exits the PCD and is vented through a process stack 37. A blower 36 is 
provided intermediate to the PCD 33 and the process stack 37. About 5% of 
the cleansed gas stream is removed through blower 36 and directed via 
first substream 38 to a cooler 39, and a second substream 40 back to the 
sorbent storage bin 31. From the cooler 39, the flue gas stream 41 is 
passed through a fluidized bed reactor 42 in which, in accordance 
herewith, it is intimately mixed and reacted with particles of soda ash, 
thereby producing sodium bicarbonate useful as a sorbent in the process. 
In operation, the flue gas stream 30 containing the fly ash and sorbent 
passes into the PCD 33 and through a filter medium where the fly ash and 
sorbent are separated. The sorbent begins to react with the sulfur dioxide 
in the gas stream as soon as the two come into contact. The reaction 
continues as the gas passes through the sorbent on the filter medium until 
about 95% of the bicarbonate has been converted by the reaction: 
EQU 2NaHCO.sub.3 +SO.sub.2 +1/2O.sub.2 .fwdarw.Na.sub.2 SO.sub.4 +2CO.sub.2 
+H.sub.2 O. 
The fly ash, unreacted sorbent, and sodium sulfate collected in the PCD 33 
are discharged through line 34 for collection as solid waste. The flue gas 
stream 35 exiting the PCD 33 is slightly cooler, about 290.degree. F., and 
about the same composition as the gas entering, except that it has been 
cleansed of fly ash and 75% of its sulfur dioxide content. Most of this 
cleansed flue gas stream, about 95%, is exhausted to the atmosphere 
through the process stack 37. 
About 5% of the clean flue gas stream 35 is removed before the process 
stack 37 with a blower 36 in order to supply carbon dioxide and heat 
energy for the bicarbonate sorbent manufacturing process. Downstream from 
the blower 36, the flue gas substream 38 to flue gas cooler 39 is cooled 
from about 290.degree. F. to about 122.degree. F., the temperature at 
which the gas stream becomes saturated with its own water of combustion. 
The second substream 40, at about 290.degree. F., is used to dry and 
convey a sorbent feed 43 from reactor 42 to the sorbent storage bin 31. 
The saturated flue gas stream 41 exits the cooler 39 and enters the 
fluidized bed reactor 42. Soda ash is metered from a storage bin 44 into 
the reactor and the gas stream is intimately mixed with the soda ash in 
the fluidized bed. Liquid water may also be metered into the reactor 
through line 46, forming a film on the soda ash particles in the bed. The 
bicarbonate reaction product is removed through stream 43, and waste gas 
is vented through line 45 after the removal of particulates. 
About 10% of the carbon dioxide entering with the clean flue gas reacts 
with the soda ash to form bicarbonate. Water from the saturated flue gas 
is also used in the formation of the reaction product. The soda ash 
adsorbs the water required for reaction and some excess water from the 
flue gas stream, resulting in a moist product. 
The carbonation reaction only occurs when an aqueous, CO.sub.2 -containing 
film forms around the soda ash particles. Such a film forms more rapidly 
when liquid water is added directly to the soda ash particles rather than 
waiting for the carbonate to adsorb sufficient water from gas stream 41. 
Accordingly, in the preferred form of the invention illustrated in FIG. 3 
liquid water is sprayed or sparged into the reactor through line 46. When 
gas stream 41 is maintained at least at 90% of saturation, greatest 
carbonation rates are obtained by thus adding about 1-2 times, preferably 
about 1.5 times, the amount of water required for stoichiometric reaction, 
to the fluidized bed in liquid form. If, on the other hand, the 
carbonating gas stream contains lesser amounts of water, it may be 
necessary to add additional liquid water to the reactor in order to 
maintain the requisite 90% relative humidity (preferably 95% relative 
humidity) in the fluidized bed. 
The unreacted carbon dioxide and water vapor, along with any inert gases, 
are used to remove the heat of reaction from the fluidized bed so that the 
temperature of the reaction mixture is only incrementally higher than the 
temperature of the cooled flue gas entering reactor 42. 
It may be noted that the clean flue gas stream 41 fed to the fluidized bed 
reactor 42 still contains about 100 ppm by volume of sulfur dioxide, which 
competes with carbon dioxide for reaction with the sodium carbonate. 
However, since the carbon dioxide concentration is about one thousand 
times greater than the sulfur dioxide concentration, the finished, dry 
sorbent contains no more than about 5% by weight of the corresponding 
sulfate salt. 
The following examples further illustrate preferred embodiments of the 
invention: 
EXAMPLE I 
Sodium Bicarbonate Production and Use in Flue Gas Desulfurization 
A 500 MW steam power plant using low sulfur western coal will, typically, 
in one hour of operation provide flue gas having the following analysis: 
______________________________________ 
% By 
Component Pounds Volume 
______________________________________ 
Fly Ash 38,200 -- 
CO.sub.2 1,140,000 
11.7 
H.sub.2 O 470,000 
11.8 
N.sub.2 4,395,000 
71.1 
O.sub.2 395,000 
5.3 
SO.sub.2 6,200 0.04 
______________________________________ 
Of the 6200 pph of SO.sub.2, typically 75% or 4,650 pph must be removed in 
order to meet air quality emissions standards. The temperature of the flue 
gas at this point is nominally 300.degree. F. 
Employing the system schematically illustrated in FIG. 3, 13,700 pph of a 
sodium bicarbonate-based sorbent of the following composition is metered 
into the flue gas stream 30 before it enters the baghouse or PCD 33: 
NaHCO.sub.3 -90%, Na.sub.2 CO.sub.3 -5% and Na.sub.2 SO.sub.4 -5%. The fly 
ash, spent sorbent, and sodium sulfate waste stream 34 is discharged from 
the baghouse in a cyclic manner and sent to a solids waste landfill area. 
The quantity of waste per hour is, nominally: fly ash--38,200 lbs; sodium 
sulfate--10,600 lbs; sodium carbonate--1,100 lbs. 
Nominally, 5% of the clean gas stream 35, or about 322,000 pph, is removed 
before the process stack 37 by means of blower 36. About 182,000 pph of 
the clean flue gas passes through heat exchanger 39 where it is cooled to 
115.degree. F. in order to saturate the gas. The saturated flue gas stream 
41, at 115.degree. F., enters fluidized bed reactor 42 where it contacts 
soda ash, which is fed in at a rate of about 8,650 pph, to produce sodium 
bicarbonate. 
The composition of the sorbent product stream 43 leaving the reactor is 
approximately: NaHCO.sub.3, 86%; Na.sub.2 CO.sub.3, 5%; Na.sub.2 SO.sub.4, 
5%; H.sub.2 O, 4%. This material is conveyed from reactor 42 to the 
sorbent storage bin 31 by substream 40 of the hot, clean flue gas stream 
removed from the blower 36. 
The following further examples were carried out in an experimental 
apparatus similar to the design depicted in FIG. 2. The reactor was a 
fluidized bed using between 20 and 30 ACFM of gas volume. The reactor was 
operated in a batch mode with solid reactant(s) equivalent to nominal 500 
gram charges of sodium carbonate. In each of the examples, the 
temperatures of the reaction mixtures peaked within 1.degree. to 
10.degree. F. higher than the reactant gas temperatures. Generally, 1% to 
10% of the carbon dioxide in the inlet gas stream was consumed in the 
reactions: 
EXAMPLE II 
Carbonation of a 30% CO.sub.2 Stream at 194.degree. F. 
Carbon dioxide gas saturated with water vapor at 194.degree. F., (30% 
CO.sub.2, 70% H.sub.2 O) was used to fluidize 500 grams of anhydrous soda 
ash. The gas flow was stopped in 20 minutes and the material in the 
reactor assayed at 87% sodium bicarbonate on a dry basis. 
EXAMPLE III 
Carbonation of a 13.5% CO.sub.2 Stream at 158.degree. F. 
A gas stream saturated with water at 158.degree. F., containing 13.5% 
carbon dioxide by volume, was used to fluidize a solid bed consisting 
initially of 306.6 grams of anhydrous soda ash and 306.6 grams of dry 
sodium bicarbonate. 87 grams of liquid water was sprayed on to the 
reaction mass over a period of 3 minutes. In 45 minutes the gas flow was 
stopped and the material in the reactor assayed at 96.5% sodium 
bicarbonate on a dry basis. The bulk density of the product was 37 
lb./ft.sup.3. 
EXAMPLE IV 
Carbonation of a 10.7% CO.sub.2 Stream at 122.degree. F. 
A gas stream saturated with water vapor at 122.degree. F., containing 10.7% 
carbon dioxide by volume, was used to fluidize a solid bed initially 
containing 221 grams of anhydrous soda ash and 442 grams of dry sodium 
bicarbonate. 62.5 grams of water was sprayed on to the reaction mass over 
a period of 2 minutes. Samples extracted from the mass after 40 minutes 
and 50 minutes assayed at 90% and 97.5% sodium bicarbonate, on a dry 
basis, respectively. The bulk density of the product was 28 lb./ft..sup.3. 
EXAMPLE V 
Carbonation of a 6.2% CO.sub.2 Stream at 122.degree. F. 
A gas stream saturated with water vapor at 122.degree. F., containing 6.2% 
carbon dioxide by volume, was used to fluidize a bed of solids with the 
same composition as in Example III. 62.5 grams of water was sprayed on to 
the reaction mass over a period of 2 minutes. After 70 minutes the reactor 
contents were analyzed and found to contain 95% sodium bicarbonate on a 
dry basis. The bulk density of the product was 37 lb./ft..sup.3. 
EXAMPLE VI 
Carbonation of an 11.3% CO.sub.2 Stream at 87.8.degree. F. 
A gas stream saturated with water vapor at 87.8.degree. F., and containing 
11.3% carbon dioxide by volume, was used to fluidize a solid bed 
containing 500 grams of anhydrous soda ash. 142 grams of liquid water was 
sprayed onto the reaction mass over a period of 110 minutes. After 260 
minutes of reaction time the reactor contents assayed 91% sodium 
bicarbonate on a dry basis. The bulk density of the product was 39 
lb./ft.sup.3. 
EXAMPLE VII 
Carbonation of a 14.3% CO.sub.2 Stream at 87.8.degree. F. 
A gas stream saturated in water vapor at 87.8.degree. F., containing 14.3% 
carbon dioxide by volume, was used to fluidize a solid bed containing 500 
grams of anhydrous soda ash. 142 grams of liquid water was sprayed onto 
the reaction mass over a period of 45 minutes. Samples extracted after 160 
and 180 minutes assayed 89% and 95% sodium bicarbonate on a dry basis, 
respectively. The bulk density of each product was 37 lb./ft..sup.3. 
The products of Example II-VII are especially suited for use as sorbents 
for flue gas desulfurization. Sodium bicarbonate thus produced has a 
density of 1/2 to 2/3 that of solution crystallized sodium bicarbonate, 
which has a bulk density of 60 lb./ft.sup.3. The lower bulk density 
facilitates conveying in the flue gas stream and more even distribution on 
the filter surfaces. The dry carbonated particles are more friable than 
their solution-carbonated counterparts. Where it is desirable to reduce 
particle size to optimize flue gas desulfurization, products so prepared 
require less energy for size reduction. 
It will be understood that various changes may be made in the preferred 
embodiments of the process described hereinabove without departing from 
the scope of the present invention. Accordingly, the preceding description 
should be interpreted as illustrative only.