CA1176033A - Fast drying sodium aluminate - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Sodium aluminates are disclosed having great utility in the control of sulfur emissions resulting from the combustion of fossil fuels. The materials contain certain additives A
preferred sodium aluminate mixture contains stabilizing amounts of gluconic acid and sorbitol.

Description

~76033 Th;s inventioll ;s directed to a method of ridding flue gas of the oxides oE sulfur and sulfuric acid utilizing an aqueous solution of sodium aluminate.
Various environnental considerations have been raised as to the introduction of sulfur oxides and sulfuric acid vapors into the air as a re-sult of the combustion of fossil fuels containing sulfur. One of the most promising chemical treatments suggested for the removal of oxides of sulfur and sulfuric acid from flue gas has been the use of an aqueous solution of sodium aluminate. This treatment is described in United States Patent No.
4,100,258. This reference suggests the use of an aqueous solution of sodium aluminate, the molar ratio of Na2O:A12O3 being greater than one. This material is then sprayed into the flue gas before it reaches the stack. A
reaction occurs between the sodium aluminate and the oxides of sulfur and sulfuric acid contained in the gas forming particulate sodium sulfate and aluminum sulfate which can then be recovered. In the following discussion all references to Na2O:A12O3 ratios are to molar ratios.
I~hile the treatment suggested in United S~ates Patent No.
4,100,258 has shown promise in the control of sulfur emissions, problems have occurred related to the speed of reaction of the sodium aluminate with oxides of sulfur contained in flue gases. In utilizing a sodium aluminate having a Na2O:A12O3 ratio greater than one, and as this reference reports which can be as great as 5, substantial free sodium hydroxide is present in the material. This material is very hydrophilic~ making the resultant additive difficult to dry and as a result extremely difficult to feed to the flue gas. In certain cases there has been a tendency of this material to even form deposits in the flue gas system due to the hygroscopic nature of the reactant material.
It would therefore be a great advantage to the art if a sodium aluminate product could be utilized which would eliminate the difficulties encountered in using prior art sodium aluminate materials. This invention ~7~iO33 is directed to the use of a sodi~m aluminate which is dried quickly in the flue gas stream and which will react much more rapidly with the oxides of sulf~r and sulfuric acid entrained in the flue gas. The invention as de-scribed below solves many of the problems encountered with the use of sodium aluminate as described in United States Patent No. 4,100,258.
THE INVENTION
It has been found that by formulating sodium aluminates with cer-tain additives, and/or utilizing sodium aluminates having Na~0:A1203 ratios of substantially one, the problems encountered with the prior art can be avoided.
It is well known that sodium aluminate having a ratio of Na2O:A1203 close to one can be prepared; see for example United States Patent No.

2,345,134. This reference discloses the preparation and stabilization of sodium aluminate utilizing up to 5% of one or more stabilizing agents such as gluconic acid, saccharates, etc. When materials of this type are employed containing a minimum amount of caustic, faster drying materials are prepared which are much more reactive to the oxides of sulfur and sulfur;c acid con-tained in the flue gas.
Additives useful in the preparation of sodium aluminate materials having low levels of excess caustic include one or a combination of a number of substances, such as Rochelle salts, tartaric acid and its salts, sac-charates, gluconic acid and its salts, gallic acid and its salts, pyrogallic acid and its salts, sugars, inverted sugars, sucrose, sorbitol, dextrin, starch, glycerols, glycols and gelatin. By using the subject materials as stabilizers, sodium aluminate containing low levels oF caustic and having ratios of Na2O to A1203 of less than 1:1.3 and preferably less ~han 1:1.1 can be prepared which are stable and which are useflll in the subject inven-tion. In the commercial practice of our invention the sodiunn aluminate pro-duct selected should generally contain as high an amount of sodium aluminate as is practical to avoid shipment charges Eor water. Generally, materials 1~76~33 of this type will contain Or from 20 - 60 and preferably 30 - 50% by weight sodium aluminate. Most preferably the sodium aluminates should contain 38 - 44% sodium aluminate by weight. The products useful in this invention should also contain a minimal excess of sodium hydroxide, generally less than a 10% excess, and preferably, only a 0 - 5% excess of sodium hydroxide.
As a practical matter, some excess NaOH must be present for stability pur-poses and thus most preferably the compositions will contain 3 - 5% excess NaOH by weight. The materials employed should have a sodium oxide-alumina ratio approximating 1.0:1Ø Generally~ however, ratios as low as this produce materials which are considered unstable. Ratios as high as 1:1.3 tend to produce satisfactory products. A ratio of from 1:1.15 to 1:1.25 is generally considered optimal for the products of this invention. In commer-cial practice, the sodium aluminates useful in this invention are stabilized by a mixture of organic stabilizers. A particularly effective composition has been found to be a mixture of sodium gluconate and sorbitol. These stabilizers will generally be present at levels of from as low as .075% to as high as 10.0% by weight of the composition. In a preferred commercial embodiment of this invelltion, sodium gluconate is present at a level of .35% with sorbitol being present as .3% by weight of the mixture.
As stated above, the stabilizers utilized are each used at levels of from 0.075% to 10% and preferably 0.1% to 5%, based on the total weight of inorganic solids in the mixturc. The percentages above are meant to indicate the amount of each stabilizer present so that up to 20% by weight total of stabilizing materials and preferably 10% by weight can be utilized in the compositions of this invention. As will be seen, the effect of water present in the mixture is unimportant so long as a stable sodium aluminate product is formed. Thus, the total amount of water in the composition can range from approximately 35% to as high as 80%.
~hile the above additives have been described for sodium aluminate formulat;ons useful in this invention, it will be seen by those skilled in ~76~33 the art that -the only major cr-iteria for the sodium aluminate is that it must dry rapidly in the conditions foulld in the flue gas stream to which it is added. Dosage of the material as sodium aluminate is described in United Patent No. 4,100,258 and need not be elaborated upon in this application.
It is sufficient to say that the material be added on a dry basis of at least .05 pound sodium aluminate per pound of entrained compound calculated as S03. The amount of sodium aluminate added to the flue gas stream in accordance with this invention can thus be described as an effective amount since it will vary with the amount of sulfur oxides and sulfuric acid present in the flue gas.
Three basic methods were developed for evaluating the products described in this invention.
1. Static Heat Test 2. Flue gas simulator

3. Spray Nozzle Test The static heat test measures the time required for complete drying of a thin film of material inside a constant heat source. Tnis served as a screening mechanism for various formulations that were tested. Formulations identified by this static heat test as faster drying than Nalco t~2, were then tested in conditions more closely simulating actual usage.
A second procedure involved feeding the formulation to a laboratory scale flue gas simulator and evaluating the deposits formed on obstructions located in the flue gas stream. The final test involved spraying the formula-tion through a nozzle and evaluating the hardness and adhesivity of tlle ~eposit.
A series of materials were prepared or obtained. These materials and their compositions are listed below.
Example 1 - Nalco #2 , sodium aluminate Vescribed in United States Patent No. ~,100,258 Contains no additional stabili er Trademark ~7~(~33 Example 2 - Sodium aluminate prepared from Example 1, but în addition containing 0.5 weight percent of a 60% aqueous solution of sodium gluconate.
Exarlple 3 - Sodium aluminate prepared from the following ingredients:
53.3% 50% aqueous solution NaQlJ

0.4% 60% aqueous solution of sodium gluconate 10.6% H20 Example 4 - A commercially available sodium aluminate believed to have the following properties:

19.5% Na2O
25.5% A12O3 Na20/A12O3 mole ratio 1:1.26 Free NaOH
These materials as is or in combination with other additives were tested in the procedures listed below.
Example 1 - Static Heat Test This test involved forming a wire loop from thermocouple wire, and forming on the loop a film of the material to be tested. The wire was then placed inside a muffle furnace, and a digital thermometer/recorder system allowed the drying rate and temperature to be recorded. The entire drying procedure could be visually observed through a cathemometer to determine the shape of the desired particles. The furnace employed was operated at a tem-perature of 500F. Nalco #2 dried at a rate of about 4 1/2 minutes at 500F., while the fastest drying formulated materials dried in only 1 I/2 minutes.
The fastest drying materials included those which were:
~1) sodium aluminates stabilized with less than 5% excess caustic;
(2) Nalco #2 containing some sort of additive which caused the film to bubble extensively due to escaping gases.

~76~33 T~BLE I

~rying t~e for a thin film Furnace temperature 750 F. (400 C.) Material Tested Tim~ tSeconds3 = _ .
Example 1 109 Example 2 77 Example 2:NH4 Cl: H20 90:05:9.5 76 Example 3 71 Example 2:60~ sodium gluconate:2-propanol (88:10:23 (2) EXample 2:60% sodium gluconate~2-propanol (94:3:3) 68 Example 2:60% sodium gluconate:2-propanol (96:2:3) 57 Example 2:60% sodium gluconate:2-propanol (97:2:1) 50 Example 2:60% sod_um gluconate:2-propanol (97:2:1) 47 Example 2:60% sodium gluconate:2-propanol (97:2:1) 90 Exa~ple 2:60% sodium glucona~e:2-propanol (98:1:1) 65 Example 2:60% sodium gluoonate:~-propanol (98:1:1) 54 Example 2:60% sodium gluco~ate:2-propanol 60 Example 2:H20 50:50 57 Exhmple 2:40% aqueous solution sodium silicate (98:2) 58 Example 2:so~ium bicarbonate (70:30) 50 Example 2:sorbitol:H2O (43:7:50) 52 Example 2:Bentonite clay (98:23 50.6 (13 Example 3:H20 (67:33) 47 E~ ?le 2:H2O (50-50) -- (2 Example 2:50~ NaOH (po~ered) (95:5) 49 Example 2:Fum~d silica (95:5) 46.75 (1) ~76033 TABIE I ~Continu~d) Material Tested Time (Seconds) Example 2:60~ aqueous solution sodium gluconate ~98:2) 46 Example 2:60~ aqueous solution sodium gluoonate ~90:10) 34 Example 2:60~ aqueous solution sodium . gluconate ~90:10) 24 Example 2:60% aqueous solution sodium gluconate (90:10) 36 Example 4 35 Exa~ple 4 28 Example 4 41 Example 4 31 Example 4 Example 4 32 (1) ~ Average value (2) - Uhable to form film ~-~L76033 T~RIE II

I Dryin~ time for a th.in film ! Furnace temperature 500n E. (260 C.) ¦ Material T~st~dLry Time (M~nutes~
¦ Exa~ple 1:60~ sc~lium gluconate:
Triton H:55 (99.4:0.5:0.1) 7 ¦ Example 2:CH3oH:Sucrose 89:10:14.9 ¦ Example 2:CH3OH:Sucrose 94.9:5.0:0.1 - 4.3 ¦ Example 2:CH3OH:Sucrose 94.9:5.0:0.1 4.2 ¦ Example 2:(Concentrated to 41% Na2Al204j 5.2 ¦ Exa~ple 2:(Cbncentrated to 41% Na2Al20~) 4.6 ¦ Example 2: 4.6 Example 2~40% sodium al ~inate solution 4.2 plus 3.2% excess NaOH:
60% sodium gluconate (99:1)] 2.6 3.1 3.5 3.4 ~.8 75.0 3.9 Example 2:Ethylene glycol:Sucrose (93:5:2) 3.5 Example 2:Sucrose g8:2 2.8 EXample 2:Sucrose 98.2 3.4 Na~1204:NaOH: 60% so~ium gluconate (~1:5:1) 2.6 NaAl2O4:NaOH: 60~ sodium gluconate (41:5:1~ 2.3 NaAl204:NaOH: 60% scdium gluconate (40:5:1) 2~6 Example 1 Conc. to 41%:60% sodLum gluconate (g9:1) 25 Example 4 2.3 EXample 4 2.1 ~xæmple 4 2.4 Flue ~as ~imulator Test _____ _, ___ T}-~ fLue gas si~lulator test utilized ~7as designed to simulate field conditions where materials of this type could be actually used. The chemical to be tested was fed into a pilot flue gas simulator system~ This system consisted of an oil-fired burner,-a radiant section, and a heat exchanger network.
The chemical was injected into the flue yas simulator nor~al to the flue gas flow through a pneumatic nebulizer chosen to approximate field chemical feed rate to a gas flow rate. A
1.5 inch by 2.5 inch target screen was placed downstream of the feed nozzle to collect deposits. The screen was centered inside the heat exchanger to allow for the most uniform air flow. The temperature of the feed noz-le, nozzle feed rate an~ distance of the screen from the feed nozzle were varied to produce hard deposits. The final conditions were: .
(1) temperature at feed nozzle 275 F.
(2) distance pf screen from feed nozzle 6 inches (3) ne~ulizer gas flow 15%
The chemical was then fed for 1 1~2 hours followed by 15 ~inute drying with the chemical off and the dr~er still on.
The data for each product treated with water is shown below in Table III. Dilution was required to enable to nebulize the product into the gas stream.

I

~176~33 T/~131.E III

Prob~ Experi~lts Probe Number Chemical Conditionof Trials EXample 1 1 2 Example 2 1 3 Example 2 Sucrose ~99:1) 3 E~ample 2 Methanol:Sucrose (89:10:1) 3 Example 2 Methanol:Sucrose (94.9:5:0.1) 3 Example 2 Ethylene glycol:Sucrose (94~5:1) Example 2 Methanol:F~rmaldehyde:
- Sucrose (93.9:5:1:0.1~ 2 Example 4 3 2 Pro~e Cbndition Key i 1 all ports sticky 2 som~ ports sticky 3 all ports dry ln -1~76(~33 Spra~ Nozzle Test This test was developed to test -the drying character-istics using a type of commercially available sPray nozzle used to introduce sodium aluminate into commercial sulfur oxide removal systems. Utilizing this system, the feed characteristics of each particular formulation could be tested. The apparatus used for this test consisted of a large propane burner/blower used to simulate the hot flue gas, and a pneumatic spray nozzle aimed at a 1 1/2 foot by 2 foot stainless steel screen. Thermocouples were used to measure the nozzle and screen temperatures. The nozzle temperature was normally about 400 F. ana the screen a~ou 200 F., since the burner could not adequately heat the large area between the nozzle and the screen. When chemical was sprayed through the nozzle, it collected on the screen. The screen ~as then evaluated for the amount and type of deposits on the screen, dryness of the deposits and ease of deposit removal from the sreen. A general rating was assigned to each product. Results of this test are shown in Table IV.

~76(~33 T~LE V

Spray Nozzle Trials ~umber Che~ical Ra-tinq of Trials .
Example 4 10 3 41% Na2Al204 containing 3.2% excess NaOH2 10 41% Na2Al204 containLng 3.2% excess NaOH2 (~a2Al2O4;NaOH; 98.2:1.8) 10 40~ ~a2Pl204 containing 3.8% excess NaOH 9 Example 4:diluted to 38% Na2Al204 9 Example 4:diluted to 32% Na2Al204 8 Example l:concentrated to 41% plus 1%
60% aqueous solution so~ium gluconate 8 Example 2:Fbrmaldehyde:Sucrose (97:1:2) 7 EXample 1:60% aqueous solution sodium glucon2te (98:2) 6 Example 3 2 Example 1 1 2 Example l:H2O (50:50) heated Example l:H2O (50:50) O 2 ~176033 ! E~ 2 I ~
A materi~]. havi.ny the following inqr~dients was ~repared:
NaOH - 50- by weight 46.82%
Alumina trihydrate 38.81%
Water 13.37~
Sodiu~ gluconate - 60% by weight .58%
¦ Sorbitol. - 70% by weight .43%
. In the formulation of this product the sodium aluminate was first prepared by heating together the caustic, alumina, and water. After cooling and with agitation, the sorbitol and gluconate were then added. This material was stable.
This material was used to neutralize S03 gas present in a commercial utility coal fired boiler. Nalco X2 as exem-plified in U.S. Patent No. 4,100,258 has previously been employed in this system with satisfactory S03 reduction, but with a problem that hard deposits formed in the system which were difficult to remove. Use of the subject chemical provided excellent S03 reduc-tion in the flue gas with no adherent de~osits being formed. This difference is attributed to the East drying characteristics and non-hygroscopic nature of the subject materia1.

s - l

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of treating flue gas with an aqueous solution of sodium aluminate to remove oxides of sulfur and sulfuric acid from the gas, the improvement comprising utiliz-ing as the source of sodium aluminate a material having a molar ratio Na20:A1203 of from 1:1 to 1:3, which is stabilized by the addition thereto of a .01 - 5% by weight of gluconic acid or a salt thereof and from .01 - 5% by weight of a compound selected from the group consisting of sorbitol and sucrose.

2. A method according to claim 1 wherein the molar ratio Na20:A1203 is from 1:1.15 to 1:1.25.

3. A method according to claim 1 wherein the sodium aluminate is stabilized by the addition thereto of 0.35%
sodium gluconate and 0.3% sorbitol.