Hot water processing

Total 1991 world production of sulfur in all forms was 55.6 x 10 t. The largest proportion of this production (41.7%) was obtained by removal of sulfur compounds from petroleum and natural gas (see Sulfurremoval and recovery). Deep mining of elemental sulfur deposits by the Frasch hot water process accounted for 16.9% of world production mining of elemental deposits by other methods accounted for 5.0%. Sulfur was also produced by roasting iron pyrites (17.6%) and as a by-product of the smelting of nonferrous ores (14.0%). The remaining 4.8% was produced from unspecified sources. 

Hot-Water Process. The hot-water process is the only successflil commercial process to be appHed to bitumen recovery from mined tar sands in North America as of 1997 (2). The process utilizes linear and nonlinear variations of bitumen density and water density, respectively, with temperature so that the bitumen that is heavier than water at room temperature becomes lighter than water at 80°C. Surface-active materials in tar sand also contribute to the process (2). The essentials of the hot-water process involve conditioning, separation, and scavenging (Fig. 9). 

Froth from the hot-water process may be mixed with a hydrocarbon diluent, eg, coker naphtha, and centrifuged. The Suncor process employs a two-stage centrifuging operation, and each stage consists of multiple centrifuges of conventional design installed in parallel. The bitumen product contains 1—2 wt % mineral (dry bitumen basis) and 5—15 wt % water (wet diluted basis). Syncmde also utilizes a centrifuge system with naphtha diluent. 

An attempt has been made to develop the hot-water process for the Utah sands (Fig. 10) (20). With od-wet Utah sands, this process differs significantly from that used for the water-wet Canadian sands, necessitating disengagement by hot-water digestion in a high shear force field under appropriate conditions of pulp density and alkalinity. The dispersed bitumen droplets can also be recovered by aeration and froth flotation (21). 

One problem resulting from the hot-water process is disposal and control of the tailings. Each ton of oil sand in place has a volume of ca 0.45 m, which generates ca 0.6 m of tailings and gives a substantial volume gain. If the mine produces 200,000 t/d of oil sand, volume expansion represents a considerable soflds disposal problem. 

Materials. Samples of dewatered crude oils were obtained from the Athabasca oil sands of the McMurray formation by extraction using the commercial hot water process (Suncor Inc.) the Bl uesky-Bu11 head formation at Peace River, Alberta by solvent extraction of produced fluids the Clearwater formation at Cold Lake, Alberta by solvent extraction of core material and the Karamay formation in Xing-Jiang, China. A summary of the physical and chemical properties of the crude oils, including chemical composition, and density-temperature and viscosity-temperature relationships, is given in Table I. 

The presence of the oil sands has been known for many years and attempts to exploit the deposits commercially go back as far as the turn of the century. These attempts included such endeavours as those by Bitumount, Abasand and others. Dr. Karl A. Clarke, who worked on tar sands over a period of many years with the Alberta Research Council, successfully developed the hot water process used in the GCOS and Syncrude operations. Currently the Great Canadian Oil Sands Ltd. plant is operating at design capacity of 45,000 BPCD and Syncrude Canada Ltd. is in the process of starting-up its operation north of Fort McMurray. 

In the present paper the various processes which have been proposed for separating the oil from the sands have been classified according to the key physical and chemical factors involved. This represents an application of concepts described previously by the author on the interfacial properties of the oil sands (2). In addition, the theories of K. A. Clark on the mechanism of the hot water process are updated in the light of new data on the flotation of oil. 

The hot water process has had the lion s share of the publicity during the past 30 years, but this is only one of several possible technologies for... 

The first three methods in Table I differ in the manner in which the oil phase is separated from the water. In the hot water process, the bitumen flecks are attached to air bubbles to effect flotation. 

This difficulty in translating what appears to be a simple technique in a beaker to a viable continuous process contributed to the failure of many subsequent pilot plants. It was not until 1967 that the first commercial plant was put on stream, using giant bucket wheel excavators to mine the sand, the hot water process to separate the oil, centrifuging of the froth to remove solid and water contaminants, delayed coking of the bitumen to produce a sour distillate product, followed by hydrofining to produce a "synthetic crude oil. 

Clark prepared a series of statements in 1944 which summarized his view of the mechanism of the hot water process (5). In 1949 he revised these statements by proposing a new mechanism for flotation of the oil (6). In the 20 years which have elapsed, a number of papers have been published which include data and observations bearing on the validity of these statements. This would therefore appear to be a suitable time for a critical review of Clarks proposals and a formulation of revised statements where required. The two sets of statements are shown below. Statements 1 and 6 were largely unchanged in the two versions. Comments on the statements are given below. 

Statement 6. Satisfactory separation of oil from sand by the hot water process is impossible unless the natural packing of the bituminous sand is completely broken down in the pulping operation and unless the pulp is subsequently dispersed in excess water. The mineral particles and oil flecks must be free to move independently of each other under the influence of the small forces upon which the process depends. 

The above is not to underestimate the role of clay in the hot water process. Tar sands of high clay content generally are difficult to process, owing partly to the tendency of clay to stabilize oil and water emulsions. In addition, polyvalent metal ions act as bridging agents between the oil and clay, particularly at low pH. The association of clay with the oil retards the attachment of air as well as increasing the density of the oil particles. This mechanism is discussed in detail in Ref. 2. 

Erskine, H.L. Suncor Hot Water Process in Handbook of Synfuels Technology, Meyers, R.A., (Ed.), McGraw-Hill New York, 1984 pp 5-1 to 5-79. 

Emulsion Capacity and Stability. The emulsion capacities of the three protein preparations are shown in Table IV. and again both the unheated and microwave treated samples were significantly superior to that of the hot water process. Although it is difficult to relate these data to those of other workers, since a wide variety of conditions are employed for measuring this property, it has generally been found that emulsifying properties are related to the aqueous solubility of proteins (7.) which further bears on the capacity of proteins to lower interfacial tension between hydrophobic and hydrophilic components. 

FIGURE 17.5 Schematic diagram of the hot water process for the extraction of bitumen from tar sands. (Reprinted from Hocking [46], with permission.)... 

In this way the useful petroleum fractions are recovered from the surface or near surface exposures of tar sand by the two currently operating hot water process extraction plants in Alberta. The production of synthetic crude oil by Alberta tar sand processors has risen from 28 million barrels (ca. 4 million tonnes) in 1978, to 77.3 million barrels (ca. 10.5 million tonnes) in 2003, which now supplies about 13% of Canada s current crude oil requirements [48]. Other processes for bitumen recovery from minable sands, such as preliminary partial sand removal with the help of cold water, followed by direct coking of the whole of the bitumen/solid residue, and solvent extraction methods have both been tested but are apparently not attractive for commercial development [49]. 

The key difference between the methods used for oil recovery from oil shales and that used for tar sands is in the methods used for separation of the organic constituent from the naturally occurring material. Oil shale processing requires the whole of the mined material to be heated to pyrolysis temperatures of 500°C or more, whereas the hot water process for tar sands extraction requires the mined tar sand (plus process water) to be heated to only around 70-80°C. Only the extracted bitumen from the tar sand, some 10-12% of the mined mass, has to be heated to ca. 500°C during the coking step to obtain synthetic crude. Because all the oil shale must be heated to pyrolysis temperatures to effect oil recovery, efficient heat transfer and... 

One of the problem areas of the hot water process for tar sands extraction arises from the clay mineral fines, which comprises from less than 1% to over 15% of the mined material. These mineral fines interfere with efficient bitumen separation in the primary separation cell and require the operation of the backup scavenger cell to maintain bitumen recovery efficiencies. Selective mining could be used to avoid the problem by leaving high fines... 

The residence times in Box 6.3 are based on riverwater being the only input of ions to the oceans. This is a simplification as there are also inputs from the atmosphere and from hydrothermal (hot water) processes at mid-ocean ridges (Fig. 6.7). For major ions, rivers are the main input, so the simplification in Box 6.3 is valid. For trace metals, however, atmospheric and mid-ocean ridge inputs are important and cannot be ignored in budget calculations (Section 6.5). 

In terms of bitumen separation and recovery, the hot-water process is, to date, the only successful commercial process to be applied to bitumen recovery from mined tar sands in North America. Many process... 

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