Results of a Techno-Economic Analysis of the Main Schemes of Loading and Storage Facilities at Kuzbass Mines

A. T. Martynenko

The loading and storage facilities of Kuzbass mines are basically arranged according to the following two principal schemes:

I. Open bunkerization, constituting a single complex (bunker–storage yard), implemented in practice in two main types:
1) conical semi-bunker scraper installations (Figs. 1, 2), and
2) trestle-type semi-bunker installations (Figs. 3, 4, 5, 6).

II. Bunkers and storage yards:
1) operating independently (Fig. 7), and
2) having a transport connection for issuing coal from the storage yard into the bunkers (Fig. 8).

If, in the first scheme, coal is loaded into railway cars exclusively by conveyor transport, through loading chutes, then in the second scheme the bulk of the coal is loaded from railway loading bunkers. The filling of the bunkers with coal by the time trains are supplied is carried out at the expense of the mines’ current production and, depending on the interconnection, even at the expense of coal located in the storage yard.

For the techno-economic analysis, let us consider the following types of equipment for loading and storage facilities, most widespread in Kuzbass, under the above-mentioned principal schemes.

Type 1 — conical semi-bunker scraper installations (Figs. 1, 2).

This type of installation is represented by two variants. The first variant (Fig. 1) provides for passing the entire output of the mine through the conical semi-bunkers of the scraper storage yard. The second variant (Fig. 2) makes it possible to load part of the coal from the current output of the mine into railway cars through loading chutes, bypassing the storage yard.

The advisability of applying one or another variant may be determined by the capital costs for the equipment and by the technological requirements with respect to coal quality.

As techno-economic calculations have shown, the second variant is more complex and somewhat more expensive, but about 30% of the coal bypasses an unnecessary rehandling operation. In the case where a mine issues several grades of coal, there may be a mismatch between the grades coming from current production and those being loaded into trains from the storage yard. Therefore the stated percentage of coal not subjected to an unnecessary rehandling operation may decrease.

Thus, the second variant is advisable for mines that work one grade of coal and dispatch it to the consumer in unit-train lots.

The loading capacity of the first type of open bunkerization is determined mainly by the capacity of the bunker pits of the scraper storage yard. In this case the loading chutes over the railway tracks have a very limited capacity (one chute about 50 t).

This capacity is necessary in the event of any delays during loading, such as, for example, removing coal from the conveyor in the event of a forced ...

Fig. 1. Scheme of open bunkerization. Type—conical semi-bunker scraper installations

Fig. 2. Scheme of open bunkerization. Type: arc-shaped semi-bunker scraper installations

stoppage of the latter or when switching the transport branch to another grade of coal.

Consequently, the amount of coal located in the bunker pit and above it, in the form of the so-called primary cone, will depend on the diameter of the pit. In addition, the scraper installation will also be able in advance, i.e., before cars are supplied for loading, to bring the required amount of coal closer to the primary cones. Therefore, the length of scraper haulage during the loading of railway cars will be small, within up to 30 m. Thus, the total amount of coal brought to the state of possible shipment proves quite sufficient, especially for mines working a single grade of coal.

The considered variants of conical semi-bunker scraper installations cannot be used for mines shipping coal to consumers in graded order—by classes. In this case the loading-and-storage devices must be supplemented with sorting equipment. Sorting plants, as is known, in order to avoid unnecessary transfer operations, are arranged directly above the loading structures. In this case railway bunkers best meet the requirements.

2nd type—trestle semi-bunker installations (Figs. 3, 4, 5, 6).

This type of installation of the open-bunkering scheme is analyzed in four variants. All variants pursue a single aim—to increase the capacity per running meter of the coal pile under the trestles, with the expectation that the coal will flow by gravity into the hoppers of the underground transport gallery, or by mechanical means without the use of manual labor. First of all, this type of loading-and-storage device may be of permanent construction, i.e., all structures made of metal and reinforced concrete, and also of simplified construction—of wood.

Despite the fact that simplified structures worsen operating conditions, they have nevertheless become very widespread in Kuzbass through the conversion of ordinary trestles.

Incidentally, it should be noted that at present the share of trestle coal storage yards at Kuzbass mines is fairly large, as can be seen from Table 1 below.

Table 1

Trestle semi-bunker installations of the variants considered are equipped with belt conveyors, because hauling coal along trestles in mine cars, at the existing output of Kuzbass mines, becomes strained and requires many people.

Trestle semi-bunker installations with one underground transport gallery are represented by a reinforced-concrete structure (Fig. 3) and a wooden one with capacious railway loading hoppers (Fig. 4).

Fig. 3. Diagram of open bunker storage. Type—elevated semi-bunker installations.
(Elevated single-gallery permanent semi-bunker)

Fig. 4. Diagram of open bunker storage. Type—trestle semi-bunker installations.
(Single-gallery trestle semi-bunker with capacity loading chutes.)

Fig. 5. Diagram of open bunker storage. Type—trestle-type semi-bunker installations
(trestle two-gallery semi-bunker)

Fig. 6. Scheme of open bunker storage. Type—trestle semi-bunker installations
(single-gallery scraper semi-bunker on a trestle)

The elevated semi-bunker installation with two underground galleries (Fig. 5) is adopted as a wooden structure. The capacity per running meter of the coal pile under the trestle is increased by 50% compared with the single-gallery installation (Fig. 4).

The single-gallery scraper semi-bunker of wooden construction has recently become widespread at Kuzbass mines.

Below we give a table of the capacity of one running meter of elevated semi-bunker installations by variants, depending on the height of the trestles, expressed in weight units (tons).

Table 2

Under Kuzbass conditions, the greatest prevalence is found in Scheme II—bunkers and storage yards—which, by relative share, accounts for about 85%.

Loading bunkers of reinforced-concrete construction, and especially wooden ones of considerable capacity, located over railway tracks or alongside the tracks, are found at almost all Kuzbass mines. But bunkers alone, unfortunately, are not capable of ensuring uninterrupted operation of the mines in shipping the mineral. Therefore, storage yards for the mineral, called emergency storage yards, have definitely been built at all Kuzbass mines.

In practice, the scheme—bunkers and storage yards—has been implemented at Kuzbass mines in two principal types.

1st type—bunkers and storage yards functioning independently, i.e., coal is loaded into railway cars independently both from the bunkers and from the storage yards.

2nd type—bunkers and storage yards with interconnection, i.e., all coal located in the storage yard is loaded into railway cars only through the bunkers.

Here, just as in Scheme I, each type may have several variants, for example: from the storage yard, coal may be loaded into cars simultaneously both through the bunkers and independently by scraper installations, through chutes or other transport machines. There are even also

variants in which there is a combined arrangement of large-capacity bunkers with trestle-type semi-bunker installations.

We believe that it is sufficient to subject to careful analysis only one variant of each type, and the one most characteristic for the mines of Kuzbass.

Figure 7 presents a variant—bunkers and a trestle storage facility of wooden construction.

Bunkers and a scraper sector storage facility of reinforced-concrete construction are shown in Fig. 8.

All the above-considered principal variants of equipment for loading-and-storage installations exist in Kuzbass in pure form or in combination. Therefore, our task in the present case is to select the most rational equipment variants on the basis of a techno-economic analysis.

As is known, of all the mines operating up to the present time in Kuzbass, at many of them coal is loaded from beneath trestles by various transport-and-loading machines. Therefore, the selected most rational equipment variants must, in the first instance, be implemented precisely at these mines.

In order to have an exhaustive economic evaluation of one or another variant of the equipment schemes under consideration, we take, wherever possible, standard mechanical equipment widely used at the mines of Kuzbass. Thus, for variants with scraper equipment (Figs. 1, 2, 6, 8), the scraper equipment is taken with the characteristics given in Table 3.

Table 3

Section A–A

Section B–B

Fig. 3. Types of loading bunkers and loading devices for coal and rock: a — [[unclear: description of first device]]; b — [[unclear: description of second device]].

Fig. 8. Scheme—bunkers and storage yards. Type—with interconnection (bunkers and a scraper storage yard)

The cost of other transport equipment—belt conveyors, feeders, transfer chutes, railroad scales, as well as erected structures—has, for all variants, been adopted according to enlarged measures based on data from Kuzbassshakhtoproekt and is given in Table 4.

In calculating operating expenses, the following was assumed:

1. Deductions for depreciation, current and capital repairs of structures: for capital installations (Figs. 1, 2, 3, 8)—8%, and for portable installations (Figs. 4, 5, 6, 7) with a limited service life—10%. For transport-and-mechanical equipment—15%; for belts—40%.

2. The service personnel and wage expenses have been calculated by qualifications, proceeding from the actual working time required for servicing the work processes, at the wage rates of operating Kuzbass mines:

a) operators of belt conveyors serving coal transport from the mine shaft to the loading-and-storage facilities work in 3 shifts;

b) operators serving conveyors for loading coal into railroad cars work in 2 shifts;

c) the number of operators of scraper winches has been adopted in accordance with mine productivity;

d) loading workers, as well as workers at stockpiles, work in 2 shifts.

The surcharge on labor for all qualifications has been taken as 37.5%.

1. The consumption of electric power by belt conveyors and scraper winches has been calculated according to the demand of the actual work of the motors under the following daily utilization:

a) conveyors for transporting coal from the shaft to the loading-and-storage facilities operate 20 hours per day;

b) operation of conveyors transporting coal into loading bunkers and cars has been adopted on the basis of unloading, over 2 hours, a unit train with a net weight of 1,400 t;

c) energy consumption for scraper winches (Fig. 6) has been calculated according to the demand of the actual operation of the winches, without full allowance for the installed capacity, which has been taken somewhat increased in case of a heavy load on the scraper devices in individual cases. For the variant (Fig. 8), power consumption has been calculated on the assumption that coal passes through the storage yard in an amount equal to 40% of the daily output of the mines.

All economic calculations were carried out for the following technical data:

1. Mine productivity: 300, 600, 900, 1200, and 1500 thousand tons per year.

2. Relative capacity of the installations: 5, 10, and 15 days.

3. The height of the coal stockpile under trestles, for the variants of trestle semi-bunker installations, bunkers, and trestle storage yards, has been taken as 6, 8, 10, and 12 m.

For the variant (Fig. 2) of a conical semi-bunker–scraper installation, capital expenditures increase by 10 thousand rubles on account of the additional conveyor and transport gallery providing direct loading of coal into railroad cars from current production; this gives an increase in expenses of 1 ruble 60 kopecks per ton of installation capacity.

Analyzing the data of the graphs (Figs. 9, 10) of capital expenditures by variants, we first of all establish the sharp distinction of the capital semi-bunker (Fig. 3), which has the highest costs in comparison with the other variants. Capital expenditures for this variant increase especially sharply with an increase in installation capacity and with an increase in mine capacity. Therefore, for practical implementation, this variant may be adopted only for mines of small capacity with a relative capac—

Table 4

Visible graph labels:

• Vertical axis: “Capital expenditures,” thousand rubles.
• Horizontal axis: “Active storage capacity,” thousand tons.

Fig. 10. Graphs of the dependence of capital expenditures by alternatives for various [[unclear: capacities]]
(stack height 6 m).

the installation capacity to 5 days, with the greatest height of the coal pile under the trestle, while observing the short-term nature of coal storage in piles.

The two-gallery semi-bunker (Fig. 5) also belongs to the number of uneconomical variants, but is quite possible for practical implementation. For this it is necessary to have a wide trestle platform and a high trestle, making it possible to form a wide coal pile beneath it. Expansion of the coal pile under the trestle is possible either by adding canopy-type devices or by installing an aeroplane-type unloader on the trestle.

Of greatest interest, from the standpoint of capital expenditures, are the variants executed according to Figs. 1, 4, 6, 8. Under all conditions the most advantageous variants are:

1. Trestle semi-bunker single-gallery scraper installations (Fig. 6), and
2. Conical semi-bunker-scraper installations (Figs. 1, 2).

It is characteristic that, with an increase in the relative capacity of the installation, the difference in capital expenditures for these variants decreases. It must be assumed that, when the installation capacity is within limits close to a monthly reserve, the variant of conical semi-bunker-scraper installations (Figs. 1, 2) will come out in first place. Comparing the trestle semi-bunker single-gallery installation (Fig. 4) with the bunker-scraper variant (Fig. 8), we note that the former is more economical only for low mine output and small relative installation capacity. In particular, with a 5-day reserve, for mines of 600 thousand tons, the capital expenditures for both variants are the same, and subsequently, with an increase in the capacity of the installation and in the output of the mines, the variant of trestle semi-bunker single-gallery installations (Fig. 4) begins to yield even to the bunker-trestle variant (Fig. 7).

Comparing all the trestle variants with one another (Fig. 11), depending on the height of the coal pile under the trestles and the output of the mines, we observe an interesting picture of the displacement of the bunker-trestle variant (Fig. 7) relative to the variants of trestle semi-bunkers (Figs. 3, 4, 5). Thus, for example, with an increase in mine output at the smallest heights of the coal pile under the trestles, the bunker-trestle variant (Fig. 7) is more advantageous in terms of capital expenditures than single-gallery and two-gallery trestle semi-bunkers (Figs. 3, 4, 5). Or, for example, this same variant is more expensive than the capital trestle semi-bunker (Fig. 3) for mines with an output of 300 and 600 thousand tons, with the height of the coal pile under the trestles being respectively 6–8 and 12 m.

Thus, using the above-mentioned graphs (Figs. 9, 10, 11), it is possible to select the most advantageous variants for specific conditions. The interrelation between rational variants is determined from the graph (Fig. 11) by the coincidence of the corresponding ordinates.

Comparing annual expenditures separately for wages and electric power (Fig. 13), depreciation charges (Fig. 12), and total expenditures (Fig. 14), we observe in all cases the advantage of the variant of trestle semi-bunker single-gallery scraper installations (Fig. 6). It is characteristic that the variant—bunkers and a scraper sector stockyard (Fig. 8)—in terms of total operating expenditures, with an increase in installation capacity, approaches the variant of conical semi-bunker-scraper installations (Figs. 1, 2), whereas in terms of electric-power costs this variant is the most disadvantageous.

In terms of total operating expenditures (Fig. 14), the greatest convergence of all variants is observed for mines of low output in all 3 cases of relative installation capacity.

GRAPHS

of the dependence of capital costs by variants, for different heights of the coal stockpile and for different mine capacities

Legend:

— Storage capacity of the installation: 5 days
– – – Storage capacity of the installation: 10 days
– · – · – Storage capacity of the installation: 15 days

Vertical axis: Capital costs, thousand rubles
Horizontal axis: Stockpile height, m

For mine capacity: 300 thousand tons/year
For mine capacity: 600 thousand tons/year
For mine capacity: 800 thousand tons/year
For mine capacity: 1,200 thousand tons/year
For mine capacity: 1,600 thousand tons/year

Fig. 11

Fig. 12. Graphs of the dependence of depreciation charges and repairs by alternatives for various installation capacities (feeder height 6 m).

Vertical axis: Depreciation charges and repairs, thousand rubles.

Horizontal axis: Installation capacity, [[unclear: units]].

Fig. 13. Graphs of the dependence of the cost of energy by variants for different installation capacities
(stack height 6 m)

Visible graph labels:

• Vertical axis: Cost of energy
• Horizontal axes:
• Installation: 5-day reserve
• Installation: 10-day reserve
• Installation: 15-day reserve
• Inset graph:
• Graph of the dependence of the cost of energy by variants
• Vertical axis: [rubles] (т р as printed)
• Curves are marked by variant numbers: 1, 2, 3, 4, 5, 6, 7, 8.

Fig. 14. Graphs of the dependence of operating costs by variant for different installation capacities
(stack height 6 m.)

Thus, summing up all that has been set forth above, we recommend the following equipment variants as the most advantageous:

1. Trestle-type semi-bunker, single-gallery scraper installations (Fig. 6).
2. Conical semi-bunker scraper installations (Figs. 1, 2).
3. Bunkers and a scraper sector storage yard (Fig. 8).

All the remaining variants, as less advantageous according to the indicators adopted by us in the calculation, may be compared with one another independently. In practice, however, their use is possible in each specific case when the corresponding local conditions are present.

Knowing the state of the loading and storage facilities at Kuzbass mines, we consider it possible to recommend the most advantageous equipment variants first of all at all mines that have manual loading at trestle storage yards.

Secondarily, the recommended variants should be introduced at mines with semi-mechanized loading. When constructing new mines, we recommend selecting equipment variants on the basis of the results of the present analysis, which provides an exhaustive comparative assessment according to all the main indicators.