Ball Mills in the Energy Industry

The primary technological facilities for making use of this new technology are: equipment for ultra-fine milling (ball mills), and the supplementary equipment for supplying and combustion of coal. Technical designs for the supplementary equipment have been developed, which are essential for wheeling-out the new technology (muffle furnace apparatus, input nozzles for the coal dust, accelerating devices for igniting the primary fuel mixtures, feeders for fuel discharge, hoppers for storage, and so forth). Factories able to manufacture the new supplementary equipment already exist in Russia. The last-mentioned also produces milling equipment, and specifically ball mills for ultra-fine milling processes.

This new technology is low-cost, with a short return-on-investment cycle which will hit break-even in no more than 2 to 3 years. The additional financing costs are in producing the ultra-fine ground coal (the purchase of ball mill machinery) – the additional machinery also has a short investment payback cycle due to the economics of the fuel supply industry.

The new Plasma-fuel technology has now passed the final stages of certification – for pilot industrial use. This allows assessment of the risks of the new technology – and if required, it can be further honed to optimise its operation prior to finalising the business case which can be put to potential investors.

Converting oil-fired boilers to run on ultra-fine ground coal

The primary task is moving to rejecting the use of fuel oil by the facility in future. Of course, in places where it is available, it makes sense to change to using natural gas. However, where this is not an available option, then such facilities can be converted to run on ultra-fine ground coal. The economic result of making the change from fuel oil to ultra-fine ground coal will be in the greatly reduced cost of fuel. Over and above this, there is an environmental gain to be made – since there will be a marked reduction in the emission of sulphurous oxides into the atmosphere. This has a further economic benefit, in terms of decreased payments to be made for such emissions.

When making the changeover to using ultra-fine coal, the issue of disposal of the ash waste which it produces needs to be addressed. For facilities currently using fuel oil, this can be problematic. In the first instance, this issue could be resolved by making agreements to remove the ash and slag waste from the boiler room to nearby ash dumps or industrial sites. This process could lead to a loss of some of the cost benefits of making the changeover. But in a more positive light, the ash and slag waste can be recycled as a component in the manufacture of construction industry materials, mineral components, and similar by-products. Installing a production line for the recycling of slag and ash is not only a responsible way of negating environmental pollution – but can similarly cull in economic benefits.

This means that the issue of converting oil-fired power stations to run on ultra-fine ground coal can be easily resolved both technically and administratively. Each individual case for conversion should properly be put through a business plan, including a technical survey of the boiler equipment, and the prevailing economic situation.

Evaluating the efficiency

Energy efficiency can be determined by making a comparison with the costs of fuel oil operation (i.e. the current costs), against the projected costs of transferring the facility’s operation to ultra-fine coal (the current costs, plus the cost of additional equipment). To make these estimates for the current costs, it follows that the costs of the current in-purchasing of fuel oil should be compared against the costs of purchasing coal, plus the additional electricity costs incurred in the grinding process. Particularly concerned with this latter cost, it pays to consider the choice of grinding machinery in the light of its electrical consumption costs. It makes obvious sense to purchase machinery with the lowest energy operating costs. Furthermore, when weighing up the decision to switch from fuel oil to ultra-fine coal, the operation of installing the additional equipment needed for ignition of the ultra-fine coal must be carefully considered.

Essential equipment:

The ball mill for grinding ultra-fine coal is essential. This kind of coal-grinding apparatus to create combustible fuel is traditionally divided into several categories. Quiet-Operation Slow Ball Mills operate with a rotation speed of 16-23 revs per minute. Fast-Action Tangential Mallet Mills have an operational speed of 590 to 980 revs per minute; and there are also Medium Roller Mills which rotate at 40 to 78 revs per minute. The table of ultra-fine coal dust obtained is below, depending upon the type of machinery chosen.

  • Ball drum mills are used for grinding anthracite and bituminous coal with a milling operational range of ≤ 1.1 and low volatility required fine grinding (6… 7 %). If the raw source material to be milled includes some presence of pyrite sulfur fuel ( up to SP > 6 % ) then only ball mills can be used.
  • Hammer mills are used for brown and black coal of relatively high volatility (Vg > 30 % ).
  • Medium Roller Mills are used for grinding coals with a milling operational range of at least 1.1 Wp and humidity of no more than 16 %, with an ash content of no more than Ar 30 %