Skip hoists

Rope location Skip hoist Install date 11/02/96 Mine VGOK Shaft Central Unit INTROS MDK21... 

FIOR Process. In the FIOR process, shown in Figure 5, sized iron ore fines (0.04—12 mm) are dried in a gas-fired rotary dryer. A skip hoist dehvers the dry fines to lock hoppers for pressurizing. The fines pass through four fluidized-bed reactors in series. Reactor 1 preheats the ore to 760°C in a nonreducing atmosphere. Reactors 2, 3, and 4 reduce the ore at 690—780°C. At higher (ca 810°C) temperatures there is a tendency for the beds to defluidize as a result of sticking or hogging of the reduced material. 

Bucket elevators, skip hoists, and cranes are used for top feeding of the furnace. Retention and downward flow are controlled by timing of the bottom discharge. Gases are propelled by a blower or by induced draft from a stack or discharge fan. In normal operation, the downward flow of sohds and upward flow of gas are constant with time, maintaining ideal steady-state conditions. 

Skip Hoists These hoists, which operate on a batch rather than continuous principle, are not so widely used as in the past. However, for high lifts and extremely lumpy or hot materials, the skip hoist is still an economical and practical device. 

FIG. 21-6 Typ es of skip hoists and sldp-hoist paths. (Faiifield Engineering Co.)... 

Types of skip hoists and skip-hoist paths. (Fairfield Engineering... 

Skip hoists can be used for all granular and lump grades but are more suitable for particles greater than 100 mm. Elevators — both belt-and-bucket and chain-and-bucket types — have been used for all grades of quicklime. The system should minimise spillage within the equipment and ensure that wear on linkages caused by the quicklime is minimised. 

LKAB operates two underground mines with 17 friction hoists. Both double skip hoists and counterbalanced hoists are used with skip capacities icuiging from 20 to 40 tonnes. 

Figure 1. Model calculation method for skip-counterbaiance hoist (ieft) and doubie skip hoist (right)...

Primary results from the model regarding double skip hoists are provided in Figure 2 and Figure 3 for reahstic future depths for LKABs operations. The investigation of steel ropes... 

Figure 2. Safety factor vs. depth and skip load for double skip hoist with synthetic ropes...

Figure 6. Required friction coefficient vs. ore mass and depth for doubie skip hoist synthetic ropes...

The single drum cage hoist on which the development work was undertaken differs in many respects from the double drum skip hoists generally described in papers on catenary oscillations. Referring to these hoists, the main differences are ... 

For such installations, more energy is required to excite the catenary to larger whip amphtude and the catenary natural frequency is lower. A double skip hoist descends with an empty conveyance which is explained by D W to give less rope whip because the tension of the rope on the drum is higher than the suspended rope which results in some rope slip which reduced the oscillations. This is not generally the case for the described installation. No major difference in whip amplitudes could be observed between up and down direction. 

At the higher speed of a large skip hoist, the resonance zone is passed faster. 

Overall, the described installation is more sensitive to severe rope whip than in larger skip hoist installations. 

In Polish mining, the first major accident caused by an over-travel event, which drew attention to the problem of emergency arresting of conveyances, was the failure of a skip hoisting device in a coal mine in Katowice. 

A conventional train level with skip hoisting to surface... 

---