Abstract:
An aqueous solution suspension or emulsion containing a water-soluble or oil-soluble non-ionic emulsifying agent is useful, when spread over the load-bearing surface of a conveyor carrying bituminous sands, to act as a release agent to promote the clean separation of the tacky sands from the belt when the latter rounds the end roller of the conveyor system and unloads the sands.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a method which comprises treating the load-bearing surface of the endless belt of a conveyor system with a release agent which is operative to cause bituminous sands subsequently deposited on the belt to separate cleanly therefrom when the belt rounds the end roller of the system. 
     The invention finds application with respect to a conveyor belt of nitrile or other rubber composition used to convey bituminous sands from a storage bin to a hot water process extraction circuit for recovering bitumen from the sands. 
     Bituminous sands, when dropped onto a conveyor belt from a height of several feet, tend to adhere to the belt surface when it rounds the end roller. Some of the adhering sands remain attached to the belt and build up on it to form an uneven load thereon. Other portions of the sands drop off the belt as it returns to the starting point of the system. To give some idea of the magnitude of this latter problem, in the 125,000 barrels of bitumen produced per day facility being constructed by the assignees of this invention, it is estimated that, in the absence of a suitable release agent, a deposit of tar sand 17 feet high would be generated beneath the conveyor belt each day. Indeed, provision has been made to permit mechanical shovels to drive beneath the conveyor belt to remove this material. 
     Out of doors, the problem has been solved by applying a liquid hydrocarbon, such as diesel fuel, to the belt surface before the sands are deposited thereon, However, this prior art belt release agent cannot be used on the convey belt connecting the storage bin and the conditioning drum in a hot water process extraction plant, as the belt is housed and the danger of fire or an explosion is too great. 
     In seeking a release agent for use on this belt, a set of criteria which the agent must satisfy has been developed. More particularly, the release agent must: 
     (a) when applied to the belt in moderate volume, effectively cause the sands to release from the belt surface when it is unloading at the end roller; 
     (b) be non-flammable; 
     (c) not be harmful to the hot water extraction process; 
     (d) not be harmful to the conveyor belt material nor render repair difficult should damage occur to the belt; and 
     (e) be non-toxic and non-corrosive. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, it has been found that an aqueous solution, suspension or emulsion containing one or more non-ionic emulsifying agents, when spread over the load-bearing surface of a conveyor belt which is to transport bituminous sands, is a satisfactory agent for use on the belt. Preferably the mixture should contain a concentration of non-ionic emulsifying agent such that when the mixture is applied to the conveyor belt, at least 1000 parts of agent is added for every million parts of water. 
     Non-ionic emulsifying agents are classified by hydrophylic lypophylic balance (HLB). Water-soluble non-ionic emulsifiers have a high HLB and oil-soluble non-ionic emulsifiers have a low HLB. Both types, when dissolved in or mixed with water, give good release efficiency. The oil-soluble emulsifiers have no measurable deleterious effect on the hot water extraction process. The water-soluble emulsifiers do have detrimental effects on the process, but this may be counteracted by the addition of small amounts of sodium hydroxide. 
     Broadly stated, the invention is an improvement on the process wherein bituminous sands are deposited on and transported by an endless conveyor belt to its end, where the sands are unloaded as the belt rounds the end roller and are subsequently subject to a hot water extraction process. The improvement comprises applying to the sands-bearing surface of the belt an aqueous solution, suspension or emulsion of a non-ionic emulsifying agent, prior to depositing the bituminous sands thereon, to provide a release agent which is operative to effect clean separation of the sands from the surface during the unloading operation without significant deleterious effect on the downstream extraction process. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention has been developed by subjecting a broad range of compounds to one or both of two tests, namely: (1) a tar sand release efficiency test; and (2) a test to determine whether the use of the compound would have a seriously deleterious effect on the hot water extraction. 
     The test apparatus for release efficiency comprised a 15 ton punch press assembly. The original die set was replaced with a spring-loaded adapter designed to accommodate belting samples. A number of 6×6×1/8 inch samples of Goodyear* Rubber Company B3835 neoprene belt surfacing material were used for testing. Each sample or block of belt material was fastened in place on the adapter by means of a recessed retaining clamp to provide an exposed area of 25 sq. in. Activation of the punch press trigger mechanism forced the belt sample downward onto a tray of bituminous sands directly beneath. By maintaining a consistent depth of sands in the tray, pressure exerted was regulated by the spring tension in the adapter. Preliminary testing yielded optimum reproducibility of results at 8.8 psi with a total of nine impacts. Lateral movement of the tray allowed three repeated stamps over each of three locations on the sands bed. 
     The tray was filled with homogenized bituminous sands to a depth of 1.5 inches and levelled by guiding a straight edge along its rim. Compressed sand was discarded after each test and replenished with freshly chopped material. 
     Precoat materials requiring dissolution in an aqueous media were applied in aerosol form until the entire belt surface was wetted. 
     Tests were conducted at ambient room temperature. Belt samples were weighed before and after impacts. Values for weights of bituminous sand adhering were compared to blank determinations (employing untreated belt samples) and expressed as a release efficiency. 
     The effect on hot water extraction of release agents which were successful in the release efficiency test was tested in a laboratory-scale batch extraction apparatus. This apparatus had been used for other studies for application at the commercial level. Bituminous sand was extracted without, and in the presence of, the compounds of formulations proposed for use as release agents. 
     The extraction apparatus comprised a 2 liter capacity stainless steel vessel jacketed in a steel shroud to allow passage of heating water between the vessel and jacket. The vessel was fitted with a driven impellor for stirring the vessel contents. Bituminous sands, belt release agent and sodium hydroxide were introduced together with slurry water into the vessel. This mixture was stirred therein for a period of time; then additional flood water was added and the flotation was carried out. Following are the details of operation: 
     
         ______________________________________Composition of Mixture:  Grams______________________________________bituminous sands         500hot water (at 80° C.)                    1150sodium hydroxide         0.12belt release agent       ≃0.10Impellor r.p.m. - 60010 min. slurry10 min. primary flotationTemperature within vessel - 82° C.______________________________________ 
    
     Froth was recovered by skimming and analyzed for bitumen, water and solids by Soxhlet extraction with toluene. 
     Following are results obtained during these tests with reference to three non-ionic emulsifiers: ##EQU1## 
     
                       TABLE I______________________________________ Belt Release Efficiency______________________________________Tar Sand analysis:          Bitumen - 12.39 w 4.08          Water83.53          SolidsEmulsifying Agent          Concentration                      Release Efficiency______________________________________Distilled Water            49.9Tergitol N P 35* (HLB 15)           2000 ppm   85.2Igepal 430* (HLB 8.6)           2000 ppm   92.9Atpet 100* HLB (4.3)           2000 ppm   89.0______________________________________ 
    
     
                       TABLE II______________________________________Effect on the Hot Water Extraction Process                NaOH Wt./ Bitumen Recovery      ppm on tar                % on tar  (wt. %) PrimaryAdditive   sand basis                sand basis                          Froth______________________________________Tergitol NP 35*      0         nil       63.7(HLB-15 watersoluble)   200       nil       53.0      1000      nil       17.5      200       0.024     86.4Igepal 430**      0         nil       37.8(HLB-8.6, water/oil soluble)      200       nil       34.5      200       0.024     84.5Atpet 100**      0         nil       63.7(HLB- 4.3, oilsoluble)   200       nil       62.0      1000      nil       63.3      600       0.024     90.0______________________________________ *Trade Mark **All three additives are nonionic emulsifying agents. Tergitol NP35 is a nonylphenol polyethylene glycol ether and is available from Union Carbide Corporation. Igepal 430 is a nonylpenoxypoly (ethyleneoxy) ethanol and is available from GAF Corporation. Atpet 100 is a sorbitan partial fatty ester and is available from ICI United States Inc.