Process to Recycle and Reuse Trona and Coal Combustion Byproducts in a Coal-Fired Power Plant

Abstract

A process is developed wherein sodium carbonate is reclaimed from Trona-treated fly ash waste stream, and the fly ash rendered suitable for use as a Pozzolan. The process is a closed system wherein all separated aspects of the waste stream are reused by the generating power plant or offered as a commercial product.

Claims

1. A process whereby Trona-treated fly ash is beneficiated by water washing 1.a) results in the removal of Cenospheres by flotation separation 1.b) results in the removal of iron-laden particles by wet magnetic separation 1.c) results in the removal of carbon-laden particles by froth flotation

2. A process whereby Trona-treated fly ash is beneficiated by the removal of sodium contaminants 2.a) results in the removal of arsenic and selenium by use of reducing or oxidizing agents 2.b) results in the precipitation of sulfates and sulfites by addition of calcium chloride 2.c) salt brine after precipitation is useable as ice control media

3. A process whereby Trona, represented as sodium carbonates, is reclaimed from Trona-treated fly ash 3.a) results in capture of sodium carbonate through Solvay process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0039] The Trona treated ash is mixed with water to a 10:1, water to solids ratio. After mixing, the solids are settled and the supernatant water is decanted. The solids are then dried. After drying the ash in examples #1 and #3 are ground in a ball mill. In example #2, the magnetic portion of the ash is removed, then the ash is ground through a ball mill.

[0040] Example #1 is a fly ash resulting from a very heavy Trona dosage as indicated by the large percentage of sodium in the ash. After washing, the amount of sodium oxide in the ash was reduced from 24.17% to 3.71% and the sulfur trioxide was lower from 6.55% to 1.05%. The strength activity index (SAI) is a procedure in ASTM C311 whereby the unconfined compressive of a mortar mix of sand, cement, fly ash and water is compared to that of a mortar mix without the fly ash. In example #1, the SAI of the unwashed ash was very low and the mortar mix exhibited early stiffening, that is it set up very fast. Ball milling the unwashed ash exacerbated the fast setting times and low strength. After removing most of the Trona residue from the ash but before ball milling, the SAI did not improve much. This ash also had a good amount of carbon, which along with the increased amount of >#325-mesh sized particles lead to a high-water requirement and low strength. This sample is a good candidate for carbon removal by froth flotation, but the procedure was not performed on this sample. After ball milling, this sample produced excellent results.

[0041] Example #2 is a fly ash resulting from a low Trona dosage and with a high iron content as indicated by the low percentage of sodium and high percentage of iron in the ash. After washing, the amount of sodium oxide in the ash was reduced from 2.1% to 0.5% and the sulfur trioxide was lowered from 2.45% to 0.39%. In Example #2, the SAI of the unwashed ash was low. Ball milling the unwashed ash greatly increased the SAL After removing most of the Trona residue from the ash, the SAI was slightly better. The magnetic fraction of this sample was removed. The iron oxide content of the ash was reduced from 24.55% to 10.91%. The pozzolanic nature of coal fly ash has been attributed to the amorphous silica and alumina in the ash. Therefore, removal of the iron-rich magnetic fraction in effect increases the amount of pozzolanic silica and alumina and increases its reactivity. There is some increase in the SAI on the nonmagnetic fraction compared to the raw sample, especially after ball milling, when this sample produced excellent results. The wash water contained 0.121 mg/L of arsenic and 0.661 mg/L of selenium. After precipitating the sulfite ions with calcium chloride, the water contained 0.083 mg/L of arsenic and 0.295 mg/L of selenium.

[0042] Example #3 is a fly ash resulting from a low Trona dosage and with a medium iron content as indicated by the low percentage of sodium and medium percentage of iron in the ash. After washing, the amount of sodium oxide in the ash was reduced from 3.62% to 1.13% and the sulfur trioxide was lowered from 3.75% to 0.92%. In Example #3, the SAI of the unwashed ash was low. The unwashed ash was not ball milled. After removing most of the Trona residue from the ash, the SAI was considerably better. Ball milling this sample produced excellent results.

Example #1: High Trona-Treated Fly Ash (Lab #19614)

[0043] Chemical Analysis, Weight %, Ignited Basis

TABLE-US-00001 19614 19614ww SiO.sub.2 39.94 55.66 Al.sub.2O.sub.3 19.63 27.41 Fe.sub.2O.sub.3 03.69 05.27 Sum SAF 63.26 88.34 CaO 00.94 01.36 MgO 00.85 01.16 Na.sub.2O 24.17 03.71 K.sub.2O 01.97 02.48 SO.sub.3 06.55 01.05 Moisture 00.68 00.37 Loss On Ignition 16.56 11.31

[0044] Physical Analysis:

TABLE-US-00002 Amt. Ret. Blaine SAI (% Control) #325 Sieve cm2/g Density 3 7 28 WR 19614* 24.6 3,585 2.29 41 43 46 107 19614bm* 01.2 9,630 2.48 29 36 34 91 19614ww 41.5 3,315 2.18 47 53 53 110 19614wwbm 00.1 10,960 2.57 101 97 96 95 wwwater washed bmball milled SAIStrength Activity Index WRwater requirement *Exhibited early stiffening

Example #2: Low Trona, High Iron Fly Ash (Lab #19604)

[0045] Chemical Analysis, Weight %, Ignited Basis

TABLE-US-00003 19604 19604ww 19604m 19604mm SiO.sub.2 41.51 42.93 21.57 52.85 Al.sub.2O 21.09 21.87 10.94 25.27 Fe.sub.2O.sub.3 24.55 26.21 62.64 10.91 Sum SAF 87.16 91.01 95.15 89.03 CaO 04.05 03.79 02.20 04.61 MgO 01.03 01.03 00.57 01.25 Na.sub.2O 02.13 00.58 00.20 00.69 K.sub.2O 01.60 01.64 00.61 02.06 SO.sub.3 02.45 00.39 00.10 00.32 Moisture 00.30 00.11 00.08 00.17 Loss On Ignition 01.74 01.79 0.07 02.57

[0046] Physical Analysis:

TABLE-US-00004 Amt. Ret. Blaine SAI (% Control) #325 Sieve cm2/g Density 3 7 28 WR 19604 24.1 2,055 2.65 78 80 80 98 19604bm 00.3 3,840 2.86 91 86 90 94 19604ww 25.6 1,880 2.67 79 77 86 98 19604wwbm 00.1 4,930 2.89 78 82 90 95 19604nm 22.9 2,150 2.41 84 83 86 97 19604nmbm 00.0 5,005 2.63 91 95 101 95 19604m 44.1 3.60 wwwater washed mmagnetic nmnonmagnetic bmball milled SAIStrength Activity Index WRwater requirement

Example #3: Low Trona Fly Ash (Lab #20164)

[0047] Chemical Analysis, Weight %, Ignited Basis

TABLE-US-00005 20164 20164ww SiO.sub.2 48.08 50.52 Al.sub.2O.sub.3 19.20 20.26 Fe.sub.2O.sub.3 14.82 16.08 Sum SAF 82.10 86.86 CaO 05.61 05.95 MgO 01.17 01.27 Na.sub.2O 03.62 01.13 K.sub.2O 02.22 02.29 SO.sub.3 03.75 00.92 Moisture 00.33 00.13 Loss On Ignition 03.88 04.32

[0048] Physical Analysis:

TABLE-US-00006 Amt. Ret. Blaine SAI (% Control) #325 Sieve cm2/g Density 3 7 28 WR 20164 12.8 4,340 2.49 71 72 98 20164ww 13.4 4,365 2.46 80 84 84 97 20164wwjm 00.1 6,985 2.66 94 97 102 95 wwwater washed jmjar milled SAIStrength Activity Index WRwater requirement