Percent SO2 oxidized

It can be calculated that for a 5 percent SO2 oxidation rate using a low sulhir fuel (0.05 wt %) the resulting additional emission of particulates would be 0.03 g/k. Since the near future emission limit is 0.15 g/kWh it is clear that SO2 conversion should be low. The exact amount depends of course on the weighting factors applied for the high load points in the testing procedures. 

Table 29.1 Industrial percent SO2 oxidation in a three pass single absorption acid plant. The feed gas contains 10 volume% SO2, 11 volume% O2, and 79 volume%N2. The catalyst bed inlet temperatures are as follows bed 1 415 °C, bed 2 425 °C, and bed 3 430 °C.

Figure 29.2 Tail gas SO2 emissions as a function of overall percent SO2 oxidation to SO3 in the acid plant catalyst beds. Double contact plants or scrubbing of single contact plant tail gas is used when greater than 99% SO2 oxidation is required. Most new acid plants are now required to meet SO2 emission standards lower than the U.S. Environmental Protection Agency standard of...

Table 29.3 Industrial percent SO2 oxidation in a four pass single contact acid plant...

Table 29.4 Industrial percent SO2 oxidation in a sulfur burning four pass double contact acid plant (3 1 configuration) (after Felthouse et al., 2011) ...

The right-hand ordinate of Figure 6 expresses the reaction rate as percent of gas-phase SO2 oxidized per hour, per unit liquid water content of the cloud. Oxidation rates in these units may be compared to clear-air oxidation rates (of order 1% h l), although this comparison should be tempered by the small fraction of the boundary layer that is occupied by clouds. 

The gas stream from a sulfur burner consists of 15 mole percent SO2, 20 mole percent O2, and 65 mole percent N2- The gas stream at atmospheric pressure and 480°C enters a catalytic converter where 90 percent of the SO2 is further oxidized to SO3. On the basis of 1 mol of gas entering, how much heat must be removed from the converter so that the product gases leave at 480°C ... 

Tests without forced oxidation also demonstrated the efficacy of adipic acid. Operating a TCA scrubber with 2,000 ppm adipic acid and 6 inches H2O pressure drop, 92 percent SO2 removal was obtained at a limestone utilization level of 88 percent. By comparison, only 75 percent SO2 removal would be expected in the pilot plant at these test conditions without the additive. At this adipic acid level, the unoxidized sludge filtered to 49 percent solids at lower adipic acid levels (1,500 ppm or less), the... 

Onstream hours Fly ash loading Adipic acid concentration, ppm (controlled) Scrubber gas velocity, ft/sec Liquid-to-gas ratio, gal/Mcf Slurry solids concentration, wt % (controlled) Scrubber inlet pH (controlled) Oxidation tank level, ft Oxidation tank residence time, min Effluent hold tank residence time, min Average percent SO2 removal Average inlet SO2 concentration, ppm SO2 make-per-pass, m-moles/liter Percent oxidation of sulfite to sulfate Air stoichiometry, atoms oxygen/mole SO2 absorbed Oxidation tank pH Percent limestone utilization Scrubber inlet liquor gypsum saturation, % Filter cake solids content, wt % 1,688 High 1,300 1,700 5.4- 9.4 85 150 15 5.0- 5.1 18 2.8 8.3 93.4 2,660 4.0- 8.9 99.8 1.4- 2.4 4.9 92.6 93 86... 

Figure 8 gives the SO2 removal as a function of adipic acid concentration and spray tower inlet pH for runs made without forced oxidation and at a constant liquid-to-gas ratio of 85 gal/ Mcf. SO2 removal is sensitive to both pH and adipic acid concentration within the ranges shown in the figure. At a liquid-to-gas ratio of 85 gal/Mcf, 90 percent SO2 removal could be achieved at 5.4 scrubber inlet pH and 1,200 ppm adipic acid, or 5.0 inlet pH and 2,200 ppm adipic acid. At 4.6 inlet pH, the required adipic acid concentration is estimated to be in excess of 3,000 ppm to yield 90 percent SO2 removal. 

Therefore, it would be advantageous to operate a low pH, adipic acid-enhanced limestone or lime system with within-scrubber-loop forced oxidation which, in addition to improved SO2 removal, requires low adipic acid makeup, minimizes gypsum scaling potential, and produces a sludge with good disposal properties. Based on Figure 9, 90 percent SO2 removal can be achieved at 5.0 inlet pH and only 1,100 ppm adipic acid, or at 4.6 inlet pH with 1,400 ppm adipic acid. 

Basis One ton of SO absorbed in TCA scrubber 90 percent SO2 removal efficiency Fly-ash-free sludge, 70 percent solids Natural oxidation Wet fan, 70 percent efficient... 

The gas from either type of gasifier contains H2, CO, and CO2. About 95 percent of the sulfur is present as H2S, and the balance as COS. Other minor components include NH3 and HCN. Carbon and ash are always present, and pyrolizers also produce oils, tars and water-soluble organics. Small quantities of oxygen, SO2, and nitrogen oxides also may be present. 

This compound reacts readily In concentrated acid. Its behavior was studied In 88.92 to 98.53 percent acid (15). The reaction Is preceded by an Induction period whose duration Is Inversely related to the acid strength. In this period one can detect the formation of small amounts of SO2 due to the reduction of the acid as the hydrocarbon Is being oxidized to a carbonlum Ion. It Is possible to relate the conversion of 2,3,4-trlmethyl-pentane to the production of Ions and a chain length of 860 has been determined for this reaction (16). 

FIG. 23-3 Temperature and composition profiles, a) Oxidation of SO2 with intercooling and two cold shots. (Z ) Phosgene from CO and CI2, activated carbon in 2-in tubes, water cooled, (c) Cumene from benzene and propylene, phosphoric acid on quartz, with four quench zones, 260°C. (cZ) Mild thermal cracking of a heavy oil in a tubular furnace, back pressure of 250 psig and several heat fluxes, Btu/(ft h), T in °F. (e) Vertical ammonia synthesizer at 300 atm, with five cold shots and an internal exchanger. (/) Vertical methanol synthesizer at 300 atm, Cr203-Zn0 catalyst, with six cold shots totaling 10 to 20 percent of the fresh feed. To convert psi to kPa, multiply by 6.895 atm to kPa, multiply by 101.3. 

Sulfur oxides (SO ) include not only SO2 but also sulfur trioxide (SO ). Sulfuric acid mist and sulfates may also be derived from sulfur oxides, but they are commonly not defined as part of SO. Most of the sulfur contamination is emitted in the form of suffur dioxide with about 1 to 3 percent of sulfur trioxide mixed in. 

The results of the tests showed adipic acid to be very effective in improving SO2 removal efficiency, even when operating at chloride levels as high as 17,000 ppm. A TCA scrubber, which removed 82 percent of the inlet SO2 without the additive, yielded 89 percent S02 removal with 700 ppm adipic acid, 91 percent removal with 1,000 ppm, and 93 percent removal with 2,000 ppm adipic acid. The limestone utilization was concurrently increased from 77 percent without the additive to 91 percent with 1,600 ppm adipic acid. The observed effects thus confirmed the theoretical expectations in all respects. In addition, the tests showed no serious inteference by adipic acid on the performance of the oxidizer, operating at pH 6.1. 

Sulfite oxidation in the system bleed slurry averaged 98.5 percent, with the air stoichiometric ratio varied between 2.0 and 3.85 atoms oxygen/mole SO2 absorbed. The filter cake solids content was 87 percent. 

At 5.0 scrubber inlet pH and 50 gal/Mcf liquid-to-gas ratio, sulfite oxidation averaged 98 percent and the SO2 removal was satisfactory at 82 percent. 

It should be noted that under the operating conditions chosen for Run 951-2E, the major SO2 scrubbing species was calcium adipate because there was little sulfite available, both in liquor or solids, normally the major scrubbing species in an unenhanced lime system without forced oxidation. Higher SO2 removal than the 82 percent in Run 951-2E should be achievable by simply raising the adipic acid concentration beyond the 1,330 ppm tested. 

An SO2 removal of only 65 percent would be predicted under the same operating conditions as Run 951-2E, but without forced oxidation and without adipic acid addition. With forced oxidation and without adipic acid enhancement, the expected SO2 removal should be significantly lower than 65 percent. 

Good sulfite oxidation of 98 percent was achieved in the oxidation tank at 4.8 pH and 1.8 air stoichiometry. SO2 removal was high at 96 percent with 4.8 scrubber inlet pH, 4,140 ppm adipic acid, and 2,030 ppm inlet SO2 concentration. 

Figure 9 shows the effects of scrubber inlet pH and adipic acid concentration on SO2 removal for runs made with forced oxidation. As in Figure 8, the liquid-to-gas ratio was held constant at 85 gal/Mcf for the runs shown in Figure 9. By comparing the two figures, it is seen that forced oxidation dramatically improved the SO2 removal, especially at the scrubber inlet pH below about 5.0. For example, at 1,200 ppm adipic acid concentration and without forced oxidation, SO2 removals were 59.77, and 90 percent at scrubber inlet pH of 4.6, 5.0, and 5.4, respectively. The corresponding SO2 removals with forced oxidation were 87, 91, and 94 percent.

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