Development of a Gas-promoted Oil Agglomeration Process

Further agglomeration tests were conducted in a series of tests designed todetermine the effects of various parameters on the size and structure of the agglomeratesformed, the rate of agglomeration, coal recovery, and ash rejection. For this series oftests, finely ground Pittsburgh No. 8 coal has been agglomerated with i-octane in a closedmixing system with a controlled amount of air present to promote particle agglomeration.The present results provide further evidence of the role played by air. As theconcentration of air in the system was increased from 4.5 to 18 v/w% based on theweight of coal, coal recovery and ash rejection both increased. The results also show thatcoal recovery and ash rejection were improved by increasing agitator speed. On theother hand, coal recovery was not affected by a change in solids concentration from 20 to30 w/w%. TABLE OF CONTENTSPageExecutive Summary1Introduction2Results and Discussion2Conclusions11References12 EXECUTIVE SUMMARYThe overall purpose of this research project is to carry out the preliminarylaboratory-scale development of a gas-promoted, oil agglomeration process for cleaningcoal using model mixing systems. Specific objectives include determining the nature ofthe gas promotion mechanism, the effects of hydrodynamic factors and key parameterson process performance, and a suitable basis for size scale-up of the mixing system.As a part of the project, numerous agglomeration tests have been conducted todetermine the effects of various parameters on agglomerate size and structure, the rate ofagglomeration, coal recovery and ash rejection. For the present series of tests, finelyground Pittsburgh No. 8 coal was agglomerated with i-octane in the presence of acontrolled amount of air. During a batch agglomeration test, the progress ofagglomeration was monitored by observing changes in agitator torque while agitatorspeed was held constant. The final product was recovered by screening and thenanalyzed to determine agglomerate size and ash content.For this report, the effects of solids concentration, air concentration, and agitatorspeed on coal recovery and ash rejection were investigated. The results indicate that coalrecovery and ash rejection both increased as the concentration of air in the system wasraised from 4.5 to 18 v/w% based on coal weight. Furthermore, coal recovery and ashrejection increased when agitator speed was increased from 1450 to 1750 rpm. Althoughan increase in solids concentration produced an increase in agglomerate size and resultedin slightly lower ash rejection, it did not affect coal recovery. INTRODUCTIONResults have been reported previously of a series of tests in which theagglomeration of Pittsburgh No. 8 coal with i-octane was promoted with small amountsof air (ref. 1 and 2). Some of the tests were carried out with a 7.62 cm diameter agitatedtank using a 3.65 cm diameter impeller, while other tests were conducted with a 11.4 cmdiameter tank using a 5.08 cm diameter impeller. The tests were conducted to determinethe effects of agitation time and various system parameters on coal recovery and grade.The series of tests has been extended and the results are reported below.RESULTS AND DISCUSSIONThe agglomeration tests were conducted with coal from the Pittsburgh No. 8Seam in Belmont County, Ohio. This coal contained 5.0% sulfur and 28% ash on a drybasis. The preparation of this material and the equipment and procedure used forconducting agglomeration tests were described previously (ref. 3). All of the testsreported below were carried out with a 11.4 cm diameter agitated tank using a 5.08 cmdiameter impeller. Pure i-octane was the agglomerate or “oil” used in each test. Theparticle suspension was first degassed and then dosed with i-octane. After the suspensionwas conditioned for 5 min. with the agitator running at the desired test speed, a knownvolume of air was introduced which started the process of agglomeration. As the testcontinued, agitator speed was held constant while agitator torque was allowed to vary.The torque was measured and recorded continuously because it had been shownpreviously that changes in the torque provided an indication of the progress ofagglomeration (ref. 3). The mixing tank was cooled with an ice Table 1. Experimental conditions and results of oil agglomeration runs with 11.4 cmdiameter agitated tank and with 5.08 cm diameter impeller. Run Solids. Oil, Air, Speed, Time, Size,Ash, AshCoalabbcd No. w/w% v/w% v/w% rpm min. mmw/w% Rej., % Rec%72 30 20 4.5 1600 85 0.05-0.10 17.91 53.45 81.6473 30 20 4.5 1600 55 0.03-0.09 18.81 55.08 75.0474 30 20 4.5 1750 55 0.05-0.10 18.16 57.41 74.2275 30 20 4.5 1450 55 (flocs) 22.48 93.02 9.2177 30 20 18 1600 55 0.08-0.12 13.82 62.94 88.1578 30 20 18 1450 85 0.08-0.11 14.05 62.93 85.0079 30 20 18 1750 85 0.07-0.12 12.54 64.67 91.9880 30 20 18 1600 85 0.07-0.11 12.97 64.76 91.9181 30 20 9 1450 25 0.04-0.06 20.50 43.90 82.3982 20 30 9 1750 85 0.25-0.30 8.37 76.50 96.6383 20 30 9 1600 85 0.308.42 77.64 96.63 Treatment time following introduction of air.a Size range and ash content of agglomerates.b Ash rejected to tailings.c Coal recovery on a dry, ash-free basis.d bath to maintain the temperature of the suspension close to room temperature. At the endof a run a sample of the suspension was collected for examination with a microscope.The range of agglomerate size was noted as well as the general shape of theagglomerates. The remaining suspension was then diluted with an equal volume of waterand separated with a 250 mm screen. The agglomerated product and the tailings wererecovered separately and then dried and weighed. The ash content of the product andtailings was determined subsequently.The conditions employed and the results obtained in the present series ofagglomeration tests or runs are presented in Table 1. The following conditions werevaried amount these tests: solids concentration, oil concentration, air concentration,agitator speed, and total time of agitation after air was introduced. For each of the tests arecord was obtained of the variation in agitator torque with time, as well as an indication of coal recovery and ash rejection. Typical results are shown in Figure 1 for three runsconducted at different agitator speeds, but otherwise similar conditions including a solidsconcentration of 30 w/w%, oil concentration of 20 v/w%, and air concentration of 18v/w%. These results are generally similar to those reported previously (ref. 2) foragglomeration of Pittsburgh No. 8 coal with 20 or 30 v/w% i-octane and 9 v/w% air.The most obvious difference was a much greater drop in agitator torque when 18 v/w%air was introduced instead of 9 v/w% air. The contrast is even greater when the resultswith 18 v/w% air are compared to those with 4.5 v/w% air shown in Figure 2. After theaddition of 18 v/w% air, the large initial drop in agitator torque was followedimmediately by a sharp rise in torque signifying particle flocculation and/oragglomeration. Such was not the case with 4.5 v/w% air where the initial drop in torquedue to the addition of air was small and there was a long delay before the torque rosesignificantly. At the lowest agitator speed (i.e., 1450 rpm), the delay was especiallylong, and even after agitating the coal suspension for 55 min. after introducing air, thetorque had not changed appreciably. Subsequent examination of the product from thisrun (i.e., run 75) revealed the presence of flocs and unattached particles but notagglomerates.For the runs conducted for 85 minutes with 20 v/w% i-octane and 18 v/w% air,the effect of agitator speed on coal recovery and ash rejection is indicated by Figure 3.Both increased slightly as agitator speed was raised from 1450 to 1600 rpm and were notaffected by a further increase in agitator speed. At either 1600 or 1750 rpm,approximately 92% of the coal on a dry, ash-free basis was recovered and approximately65% of the ash was rejected. Figure 1. Results of three runs conducted with 30 w/w% solids, 20 v/w% oil, 18v/w% air, and different agitator speeds in 11.4 cm diameter tank. Figure 2. Results of three runs conducted with 30 w/w% solids, 20 v/w% oil, 4.5 v/w%air, and different agitator speeds in 11.4 cm diameter tank. Figure 3. Effect of agitator speed on coal recovery, ash rejection, andproduct ash content for runs made with 30 w/w% solids, 20v/w% oil, 18 v/w% air, and 85 min. treatment time. Figure 4. Effect of agitator speed on coal recovery, ash rejection, andproduct ash content for runs made with 30 w/w% solids, 20v/w% oil, 4.5 v/w% air, and 55 min. treatment time. The results achieved with 20 v/w% i-octane, 4.5 v/w% air, and agitation time of55 min. were much worse (see Figure 4). Since true agglomerates were not produced at1450 rpm, coal recovery at this agitator speed was almost nonexistent. With an agitatorspeed of 1600 or 1750 rpm, coal recovery was 74-75 % and ash rejection was 55-57%.A comparison of these results with the previous set of results indicates that the reducedair concentration and treatment time were detrimental.The reduced air concentration seemed to have a greater effect than the reducedtime. This can be seen by comparing the results of runs 72, 73, and 80 which wereconducted under the same conditions except for air concentration and treatment time.The differences in conditions and results are shown below.Run No.Air, v/w% Time, min. Ash Rej., % Coal Rec., %80188564.891.9724.58553.581.6734.55555.175.0The above data indicate that the reduction in air concentration from 18 to 4.5v/w% produced a relatively large drop in coal recovery and ash rejection, whereas thereduction in treatment time from 85 to 55 min. produced relatively small changes in coalrecovery and ash rejection.A combination of the results of runs 72 and 80 with those of run 64 conductedpreviously with 9 v/w% air showed that coal recovery and ash rejection both increasedgradually as air concentration increased (see Figure 5). Figure 5. Effect of air concentration on coal recovery, ash rejection, andproduct ash content for runs made with 30 w/w% solids, 20v/w% oil, and 85 min. treatment time using an agitator speedof 1600 rpm in 11.4 cm diameter tank.