CA1188644A - Control of process aid used in hot water process for extraction of bitumen from tar sand - Google Patents

Abstract

"CONTROL OF PROCESS AID USED IN HOT WATER PROCESS
FOR EXTRACTION OF BITUMEN FROM TAR SAND"
ABSTRACT OF THE DISCLOSURE
The hot water process is sensitive to the nature of the tar sand feed, which varies. An alkaline process aid, usually NaOH, is normally added to the conditioning step of the process and is needed to obtain good bitumen recovery from most tar sand feeds. The invention is based on the discovery that, for a particular extraction circuit used, there is a single value of free surfactant content in the aqueous phase of the process slurry which will yield maximum primary froth recovery regardless of the type of tar sand feed used. The process in accordance with the invention therefore comprises: (a) determining, for a single tar sand type and the extraction circuit used, the free surfactant content in the aqueous phase of the slurry, which will yield the maximum primary bitumen froth recovery; (b) monitoring the free surfactant content in the aqueous phase of the slurry during subsequent processing of various types of tar sand feed in said circuit; and (c) varying the process aid addition to the slurry as the nature of the tar sand feed varies, to maintain said free surfactant content sub-stantially at the level which leads to maximum primary bitumen froth recovery.

Description

8~4~

2 This invention relates to an improvement of the hot water

3 process for extracting bitumen from tar sand. More particularly, it

4 relates to process control, specifically control of process aid addition, whereby primary bitumen Froth recovery may be maximized, in spite of 6 the changing nature of the tar sand feed.

8 Tar sand, also known as oil sand and bituminous sand, is g now well recognized as a valuable source of hydrocarbons. There are presently two large plants producing synthetic crude from the tar sands 1l oF the Athabasca region of Alberta. In these operations, the tar sands 12 are first mined and the bitumen is then extracted by a process called the ho-t water process. The extracted bitumen is subsequently upgraded 14 by refinery-type processing to produce the synthetic crude.
The tar sand is a mixture of sand grains, connate water, 16 fine minerals solids of the particle size of clay minerals, and bitumen.
17 It is commonly believed that the connate water envelopes the grains of 18 sand, the fine solids are distributed in the water sheaths, and -the 19 bitumen is trapped in the intersti-tial spaces between the water-sheathed grains.
21 The hot water process is now well described in the patent 22 and technical literature.
23 In broad summary, this process comprises first conditioning 24 the tar sand, to make it amenable to flotation separation of the bitumen from the solids. Conditioning involves feeding mined tar sand, hot 26 water (180F), an alkaline process aid (usually NaOH), and steam into 27 a rotating horizon-tal drum wherein the ingredients are agi-tated together.
28 Typically, the amounts of reagents added are in the following proportions:
29 tar sand - 3250 tons hot water - 610 tons 31 NaOH - 4 tons (20% NaOH) 1 Enough steam is added to ensure an exit temperature of the mixture from 2 -the drum of about 180F. The residence time in -the drum is typically 3 about 4 minutes.
4 During conditioning, -the mined tar sand (in which the bitumen, connate water and solids are -tightly bound together) becomes 6 an aqueous slurry of porridge-like consistency, wherein -the components 7 are in loose association.
8 The slurry leaving the drum is screened, -to remove oversize g material, and then diluted with additional hot water. The product typically comprises 7% by weigh-t bitumen, 43% water and 50% solids. I-ts 1l temperature is typically 160 - 180F.

12 The diluted slurry then is transferred into a large separation vessel having a cylindrical upper section and conical lower section. Here the slurry is retained for about 45 minutes in a quiescent condition. Most of the sand sinks to the bottom and is discharged, 16 together with some fines, water, and bitumen, through an outlet. This discharge is discarded as tailings.

18 The bitumen present in the separation vessel exists in the 19 form of globules, some of which attach themselves to air bubbles en-trained in the slurry during conditioning. The aerated bitumen tends 21 to rise through the slurry and is recovered as a froth by a launder 22 extending around -the upper lip of the separation vessel. This froth is 23 called primary froth. Typically, it comprises:

24 66.4% bitumen 8.9% solids 26 24.7% water 27 Not all of the bitumen becomes sufficiently aerated to rise 28 into the primary froth product. Much of this bitumen, together with 2g much of the fines, tends to collect in the mid-section of the separation ves.sel. This aqueous mixture is termed "middlings".

The middlings are wi-thdrawn from the vessel and are fed 2 into subaerated Flota-tion cells. Here the middlings are subjected to 3 vigorous agitatlon and aeration. Bitumen froth, termed "secondary froth", is produced. Typically, this froth comprises:
23.8% bitumen 6 17.5~, solids 7 58.7% water 8 It will be noted that the secondary froth is considerably 9 more contaminated with wa-ter and solids than the primary froth. One seeks to minimize this contamination, as the froth stream requires down-11 s-tream trea-tment to remove solids and water, before it can be fed to 12 the upgrading process.
13 It is desirable -to operate the process so that as much of 14 the bitumen as possible reports to the primary froth. The efficiency with which bitumen is collected as primary froth is a measure of -the 16 success with which the entire bitumen in the tar sand feed has been 17 brought to a condition amenable for spontaneous flotation. For this 18 reason, we consider maximizing primary recovery as optimizing the entire 19 process.
Now, the tar sand feed to the hot water process is not 21 uniform in nature. Its properties vary in accordance with factors 22 such as bitumen content, fines content, nature of the coarse solids, 23 extent of ageing and weathering after mining, and the chemical nature 24 of the bitumen. This variation in properties of the feedstock requires that the processing conditions be altered from time to time with a view 26 to maximizing primary froth recovery. Some optimizing techniques, such 27 as regulating middlings density within a preferred range or main-taining 28 the temperature with a preferred narrow range, can assist in improving 29 recovery over a narrow variation in -the nature of the tar sand feed.
But there is a need for identification of a parameter which can be 31 monitored and used to maximize primary froth recovery over a wide range 32 of different tar sand types.

1 At this point, i-t is useful to review the role of the "process 2 aid" , as it was understood in the past. The originator oF the hot water 3 process, Dr. Karl Clark, noted tha-t the tar sand was acidic in nature 4 He -taught the need to add an alkaline process aid, such as NaOH, to adjust the pH of the drum slurry to near neu-tral condition, in order to improve 6 bitumen recovery in the primary separation s-tep. Later inves-tigators 7 taught -that i-t was desirable to main-tain a slurry p~l in -the range of 8 about 8 - 9, to maximize bitumen recovery.
g More recently, Dr. Emerson Sanford, a co-worker of the present applicants, set forth in Canadian Patents 1,100,074 and 1l 1,094,003 that the role of the NaOH was to produce surfactants in the 12 slurry by reac-tion ~ith carboxylic and sulfonic acid substituents present in the bi-tumen. He submitted that it was surfactants that were needed to condition the tar sand to free the bitumen from the other tar sar,d components and render said bitumen amenable to air attach-16 ment. He further taught that the level oF -Fines would affec-t the surfactant requirements. In summary, he taugh-t that:
18 (1) some process aid was needed for good primary recovery;
19 (2) the process aid functioned by generating surFactants within the slurry, which surfac-tants were required 21 to maximize bitumen recovery; and 22 (3) different tar sand types, having different fines contents, 23 would require different quantities of NaOH in order to 24 achieve maximum primary froth production.
However, up to this time there has been no single means 26 identified in the prior art which would enable one to control the process 27 aid addition to obtain maximum primary froth recovery while proces~sing 28 various types of tar sand ore, such as low grade (i.e. high fines) ore, 29 marine ore, aged ore, and overburden-contaminated ore.

. ~

2 The present invention is based on the discovery that there 3 is a critical level of free surfactant in solu-tion in the aqueous 4 phase of the drum slurry which always is required to obtain maximum recovery of bitumen from the tar sand in the primary froth.
6 Having made this discovery, a process has been evolved 7 comprising the following steps:
8 (1) first determining, For the extraction apparatus used, g what the a-Foresaid critical level is for one tar sand -type feeds-tock;
11 (2) then es-tablishing from time to time the free surfactant 12 content in the aqueous phase of the drum slurry as different tar sand type feedstocks are processed; and (3) varying the process aid addi-tion to the slurry as the nature of the feedstock changes, to main-tain said free 16 surfactan-t level s.ubstantially at tha-t value which results in maximum primary froth recovery.
18 The free surfactant content in the aqueous phase of the 19 drum slurry may be established either by:
(a) measuring i-t directly, or 21 (~b) measuring the ~Free surfactant content in another of the 22 process streams associ`ated with the hot water process 23 (provided that such content is indicative of the free 24 surfactant content in the aqueous phase of the drum slurry - this would, for example, be true of the 26 middlings and tailings streams from the separation 27 vessel).

2 Figure 1 is a schema-tic of a hot water process circuit of 3 the -type used commercially;
4 Figure 2 is a side view of a laboratory apparatus used to develop the data underlying -this invention - it has previously been 6 established that -there is a direct correlation oF the results obtained 7 using the appara-tus of Figure 2 with the results obtained using the circuit 8 of Figure l;
g Figure 3 is a plot for various tar s.and type samples of lo primary bitumen froth recovery (%) against free surfactant concentration 11 in secondary tailings from the circuit usedJ and 12 Figure 4 is a side view of the foam fractiona-tion column and 13 nitrogen humidifier used to concentrate surface active compounds from 14 centrifuged secondary tailings.

DESCRIPTION OF THE PREFERRED EMBODIMENT
16 The invention has been developed using the laboratory batch 17 extraction unit shown in Figure 2. The unit comprised a steel pot 1 18 surrounded by a heating jacket 2 supplied with temperature-controlled 19 hot water. An agitator 3 and sparger 4 extended into the pot l,as shown.
21 Previous experience with use of the laboratory unit had 22 shown that its performance, when treating tar sand in accordance with 23 the hot water process, correlates fairly closely with the performance 24 of -the commercial plant operated by the assignees. and ou-tlined in Figure 1.
26 The work which produced the invention involved taking a 27 single tar sand feedstock and subjecting portions of this feedstock to 28 the hot water process in the Figure 2 unit, keeping all conditions the 29 same except for the amount of NaOH added. The free surfactant conten-t in -the secondary tailings from the uni-t was moni-tored in the manner 31 described below. The results are plotted in Figure 3.

1 More particularly, the common conditions used for all runs 2 were as follows:
3 A charge of 500 g of tar sand, 150 ml of water (82C), 4 and differen-t amounts of NaOH , were introducecl into -the pot 1. Hot water was circulated through the jacket 2 to bring the charge to 82C
6 and maintain it there. Once the charge was at temperature , it was 7 agitated with the agi-tator 3 for 10 minu-tes at 600 rpm's while simul-8 taneously introducing air into the charge at 7 ml per second through 9 the sparger 4. The air was then switched off and the mixture flooded with 900 ml of hot water (82C). Mixing with the agitator 3 was con-11 tinued for a further 10 minutes. The agi-tator was then switched off.
12 The produced primary froth was skimmed ofF the surface of the mixture 13 and weighed.
14 The residual mixture was then subjected to secondary separation.
More particularly, it was agitated at 800 rpm for 5 minutes with air 16 sparging at the rate of 4 ml/sec. The secondary froth produced was 17 s.kimmed off.
18 The procedure as set forth above was practised on a single 19 tar sand feedstock using various NaOH amounts as se-t forth below.
Table 1 gives the tar sand characteristics. Table 2 gives the extraction 21 data for one of the tar sand types.

22 TA~LE 1 -23 Tar Sand Properties 24 Oil l~ater Solids Fines Content Content Conten-t Content (< -44 ~m) 26 Tar Sand Comments % (w/w) % (w/w) % (w/w) % (w/w solids) 27 Rich Fresh 13.1 2.7 84.2 lo.9 28 Marine Fresh 8.7 6.4 84.9 13.1 29 Aged 70 days 8.7 6.4 84.9 13.1 Aged 90 days 8.7 6.4 84.9 13.1 2Extractlon Da-ta for the Marine Tar Sand 3_ Aged 70 Days 4 NaOH Mass Pri`mary Fro~h Composition Percent Level and Wall Fro-th (% w/w) Primary 6 (% w/w Tar Sa~l(g) _ Oil Water Solids Recovery 7 0-00 1.0 1.5 95.9 2.6 2.4 8 0.04 10.7 3~.9 62.8 2.3 24.5 9 0.08 22.5 56.5 39.6 3.0 51.5 0.16 32.2 74.8 22.5 2.7 73.7 11 0.20 27.3 73.0 24.1 2.8 62.5 12 0.24 20.9 65.4 32.2 2.5 47.8 13 Calculation of Primary Recovery 14 Pr1mary Recovery = wt. Bitumen in Primary Fro-th x 100 wt. total Bitumen in the Tar Sand Surfactant Determination 16 Secondary tailings, as obtained above, were cen-trifuged 17 at 15,000 G to remove suspended solids. An aliquot (50 mL) of the 18 supernatent was then titrated with 0.05 N hydrochloric acid. The titra-19 tion was monitored by measuring pH and specific conduc-tances. From such titrations, the concentration of total car60xylic acid salts 21 (ilncluding surface active and non-surface active species) was obtained 22 in the following manner.
23 In order to determine the amount of surfactant in the secondary 24 tailings samples, use was made of -the tendency of surfactants -to con-centrate at interfaces. To this end, a second aliquot (200 mL) of the 26 supernatent was foam fractionated in a 300 mL cylindrical vessel equipped 27 with a nitrogen sparger, as shown in Figure 4. We used a method similar 28 to that of Bowman (see "Molecular and Interfacial Properties of Athabasca 29 Tar Sands", Proc. 7th World Petroleum Congress, 3 , 583 - 604, 1967).
The nitrogen sparge was maintained at a (low) level which produced the 31 smalles-t bubble sizes in the foam. Frac-tionation was continued until 1 the surface tension of the residue reached a limiting value near that 2 of pure water, as determined by a maximum bubble pressure technique.
3 Aliquots (50 mL) of the fractionate and residue were each titrated to 4 determine -the -total carboxylic salt content.
The surfac-tant concentration was determined as follows.
6 The fractionate con-taining collapsed foam yields a salt concentra-tion 7 (CF):
8 C = CnFs + CsF (1) g where CnFs and CsF are the concentrations of non-surface active and lo surface active salts in the fractionate respectively. The residue 1l contains only non-surface active salts hence 12 cR = CnRs (2) where the superscripts indicate the residue portion. At equilibrium the 14 concentrations of non-surface active salts will be very nearly equal in the aqueous phases of the foam and in bulk solution:
16 CnFs = C

17 Combining equations (1) - (3):
18 cF = CR + cF

19 As CF and CR are determined by titration the surface active salts are obtained as CsF from equation (4). With appropriate volume corrections 21 the concentration of free surfactant present in the original (secondary 22 tailings) sample was obtained.
23 An example of these calculations is now given for one 24 extrac-tion of the aged (70 day) marine tar sand.

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Taking the 70 day aged marine ore processed at a sodtum 2 hydroxide addition level of 0.08 weight percent we have the following 3 da ta 4 Total secondary tailings sample volume = 1080 ml Fractionate carboxylate salt con-tent determination:
6 Total fractionated volume = 202 ml = V
sample 7 Fractionate volume = 53 ml = V
fractionate 8 Aliquot volume = 52.5 ml = V .
allquot g Volume of acid titrated = 0.52 ml = V~
Normality of acid = 0.0571 N= N

1l Therefore concentration of carboxylate salts = NHcl V
aliquot 12 = 5.7 x 10 4N
13 = cF in equation (4).

14 Residue carboxylate salt conten-t determination:
Residue volume = 148 ml 16 Aliquot volume = 50.0 ml = Valiquot 17 Volume of acid titràted = 0.37 ml = V
18 Normality of acid = 0.0571 N= N

19 Therefore concentration of carboxylate salts = NHCl . V
Valiquot = 4.3 x 10 4N
21 = cR in equation (4).
22 From equation (4):
23 CsF = 1.4 x 10 N

1 This is the concentration present in -the fractionate sample VfraCtionate~ ~
2 Therefore the carboxylate surfactan-t concentration in the total -fractionated 3 sample (and hence in the original tailings sample) is then C = Cs Vfractionate = (1.4 x 10 N)(53 mL
Vsample (202 mL) = 3.7 x 10 5N

6 The de-termination of free surfactant content has been 7 described with respect to making the measurements on the aqueous phase 8 of the secondary tailings. The same measurements may be made with the g same benefit on other aqueous streams of the hot water process, such as the drum slurry, the primary separation vessel slurry, the primary 11 tailings and the like, the only difference being the degree of dilution 12 of the dissolved components.
13 When the phrase "aqeous phase of the slurry" is used in 14 the claims hereunder, it is intended that the phrase will be interpre-ted to encompass these various hot water process aqueous streams.
16 The free surfactant content data have been plotted against 17 primary recovery to provide the curves shown in Figure 3. It will be noted18 that there is a curve developed for each feedstock of Table 1, which has 19 been treated with varying quantities of NaOH addition. The curve passes through a maximum. Thus maximum primary recovery occurs for only one 21 value of free surfactant. Both below and above that value, the primary 22 recovery diminishes. To summarize, for a given circuit, the maximum 23 primary recovery for various tar sand feedstocks always occurs at sub-24 stantially the same free surfactant concentration in the process water.
This finding makes it possible -to operate a commercial 26 circuit in accordance with the following steps:

1 (a) determine, for a single -tar sand type and the extraction2 circui-t used, the free surfactant, in the aqueous 3 phase of the slurry, which will yield the maximum primary bitumen froth recovery;
(b) monitor the free surfactant content in -the aqueous 6 phase of the slurry during subsequent processing of 7 various types of -tar sand feed in said circuit; and 8 (c) vary the process aid addi-tion -to the slurry as the nature 9 of the tar sand feedstock varies, to maintain said free surfactant content substantially at the level 11 which leads to maximum primary bitumen froth recovery 12 as found for the tar sand in (a).

Claims (2)

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

1. In the process of extracting bitumen from tar sand of varying nature using the hot water process in an extraction circuit, wherein the tar sand is slurried in a conditioning drum with hot water and alkaline process aid, agitated, and then retained in a quiescent condition to produce primary bitumen froth, the improvement comprising:
determining, for a single tar sand type and the extraction circuit used, the optimum free surfactant content in the aqueous phase of the slurry, which will yield the maximum primary bitumen froth recovery;
monitoring the free surfactant content in the aqueous phase of the slurry during subsequent processing of various types of tar sand feed in said circuit;
and varying the process aid addition to the slurry as the nature of the tar sand feed varies, to maintain said free surfactant content substantially at the level which leads to maximum primary bitumen froth recovery.

2. The process as set forth in claim 1 wherein:
the optimum free surfactant content in the aqueous phase of the slurry is determined by operating the process with one tar sand feed type using different amounts of process aid addition to establish the amount which provides substantially maximum primary froth recovery.