Stacking, Blending & Reclaiming Bed Blending Efficiency – Adding Value with Stockyard Systems
The drive of end-users towards efficient raw-material sourcing leads to a growing number of often worldwide spread sources with varying material characteristics. Yet, new boilers, kilns or blast furnaces require a feed material quality of even increased consistency to achieve high process efficiency and product quality.
The drive of end-users towards efficient raw-material sourcing combined with the need for a feed material quality of even increased consistency leads to new challenges for material blending and homogenising. Centralised blending and homogenising facilities may be a solution to reduce the cost impact on the production process. The example of a coal handling system with the coal provided by road trucks from up to eight different mines with a wide variety of coal characteristics is used to discuss from a stockyard designer’s as well as an equipment supplier’s point of view the challenges related to the requirement of high product homogenisation.0
The example investigated in this paper relates to a recent project in South East Asia. The conclusions drawn, however, may be applicable also to projects in other parts of the world. With the growing demand of developing economies, new technological developments in the raw materials market such as the fast growing use of unconventional gas in the US, and the recent financial challenges to the world economy the raw material prices become more and more volatile. This, in combination with an underlying long term trend towards higher prices, leads increasingly to short-term supply contracts and opportunity driven sourcing (Fig. 1 and Table 1).
That does not only pose a challenge to the procurement department but also to operations. Raw material coming in with varying characteristics from frequently changing sources makes planning of efficient production processes more difficult, in particular looking at the high requirements of most modern production systems like boilers with less than 40 percent energy efficiency, blast furnaces or cement kilns just to name a few (Fig. 2).
The increased number of raw material sources and hence material qualities leads to growing space requirements and the need for more sophisticated stockyard technologies. This, in combination with a worldwide trend towards stricter regulations on emissions such as dust and noise calls for centralisation of blending and homogenising facilities as a way to avoid too steep cost rises as well.
Challenge and Opportunity: Changing Requirements to Stockyards
In a logistics chain the primary logistical task of a stockyard is to buffer the material flow. The various modules of a transport chain, characterised by:
- different batch size (transport capacity),
- different transport sequence, and
- different common transport distance,
such as trucks, trains, river barges or large ocean vessels can be unlinked by stockyards buffering the material in between. Thus, the transport modules can operate fairly independently and waiting times are reduced (Fig. 3).
Further tasks of stockyards may be blending and homogenising of material (Fig. 4). At this point the difference between “blending” and “homogenising” should be reiterated, since until today the terms still are often used rather as synonyms. “Blending” is the process of mixing two or more different materials aiming at receiving a blend with a new average level of certain parameters. It is done for instance in ports if the material reclaimed from different piles is layered on a conveyor before feeding the material into the vessel. The layering is disturbed and the material is mixed at the conveyor transfer points. Usually the total of the mix in the vessel then has a certain predicted average quality. The variation of the characteristics relative to the average over a period of time is often of lesser importance.
Mine stockyards often serve for blending of raw materials with often widely varying characteristics originating for instance from various mining faces within one mine or from different mines within an area. The major focus here is on blending. Selected parameters of the blend have to meet the specification in average and within a certain fluctuation range. The quality is regularly checked through sampling as per one of the internationally accepted standards.