High density solids pump extinguish subsurface deposit fires

Aichtal, (PresseBox) - In the Kosovan open-cast coal pits of Mirash and Bardh, from which 97% of the raw materials for generating power for the province of Pristina are produced, the brown coal deposits are slowly diminishing. At an annual output of approximately 6.5 million tonnes, the areas currently used will probably be out of coal by 2011. Further subsurface smouldering fires are reducing the coal deposits. A mobile Putzmeister mixing and pumping plant is fighting against the fires.

The brown coal produced in Kosovo is currently only just sufficient to handle the serviceable power station capacities of the region. An increase in mining capacity is not, however, possible due to technical problems with the equipment and due to improper handling of the deposit. The slopes, which are often too steep, and the layer of brown coal burning below the surface damage the deposits and thus destroy important resources.

Self-ignitioned fire

The subsurface deposit fires caused by spontaneous combustion are caused by the tunnels once made through in the brown coal layer, which were subsequently not properly sealed.

The spontaneous combustion fires are caused when oxygen is “pumped” into the brown coal layer as a result. The supply of oxygen then triggers oxidation reactions in the brown coal. If there is sufficient oxygen, it could heat the brown coal to such an extent that the layer itself ignites.

The uncontrollable subsurface fires have since formed unidentified voids in the open pits, resulting in a loss of stability of the slopes and side walls of the open pit. Heavy trucks such as diggers and cranes consequently slip and fall into the voids that suddenly appear on the earth's surface.

To save the resources and to reduce the release of CO2 and other toxic gases, Putzmeister worked in collaboration with Boss Pro-Teck to develop and supply a mobile mixing and pumping system, designed for use in open pits to deal with the subsurface deposit fires in the Kosovan brown coal area.

Fire-fighting with pumped past

A mixture of fly ash, binder and water are used to fight the fires. The mixture is pumped in via special holes and distributed around the source of the fire. The fly ash required is supplied by the power plants in the area.

In detail, the combined mixing and pumping system consists of the following components:
- a material collection container as a temporary silo with trough chain conveyor
- a mobile screw conveyor
- a container platform (20 ft) with installed KOS high-density solids piston pump including attached flow-type mixer, 55 kW hydraulic power pack and 80 kW power pack and compressor
- an office container (20 ft)
- a pipe container (20 ft) for a delivery line approximately 300 m long made up of ZX pipes, hoses and couplings.

Plant for mixing and pumping is easily to move

During the system design process, particular attention was paid to providing the individual components with the best possible mobility and transportability, so that the entire system can be relocated quickly with the help of a crane and tracked vehicles. For this purpose, a 20 ft transport slide was developed, on which the container parts can be lifted and moved to their new site of use with a pretensioned track.

The core of the mixing and pumping system is formed by a KOS transfer-tube-controlled high density solids pump on the container platform. The particular feature of the KOS series is the S transfer tube. The S transfer tube creates a secure connection with the delivery line when switching from suction to pressure stroke and thus enables operation that is practically continuous. Individual foreign bodies can thus be easily conveyed up to a particle size of 80% of the outlet diameter. The machine is almost identical to the Putzmeister BSM 1000 E (“ELEFANTINO”) piston pump that has been used for years in coal mining to pump concrete and building materials. The compact pump unit is driven by a separate 55 kW hydraulic power pack.

The mixing and pumping system is designed for a capacity of 17 m³/h. When determining the mixing and pumping process, the ever-changing distances between the power stations and sites of use were taken into consideration. The fly ash is supplied to the open pit by an off-road tractor and trailer unit. To enable a continuous mixing and pumping process, the discontinuously supplied dry, free-flowing fly ash is first tipped into a material collection container with a volume of approximately 20 m³ and from there into a flow-type mixer via a trough chain conveyor and downstream screw conveyor. After adding water and binder, you have a pumpable medium, which can be conveyed by the Putzmeister high density solids pump through a pipeline with a cross section of 125 mm into the holes created to put out the fire.

Source of the fire circled round by bore holes

The selection of suitable places to make holes is determined before the boring process begins with the help of thermal imaging cameras and – where the generation of heat and gas allows – with mapping. The boring rods on board is capable to reach depths up to 40 m, often boring is no deeper than 12 m below surface. The holes are positioned around the source of the fire below the surface and then refilled with the pumped material. The small distance between the holes results in a wall, similar to a palisade wall. The objective of drilling and filling these holes is to prevent further spreading of the fire and the supply of fresh oxygen. This prevents the fire from spreading to other layers. If subsurface tunnels or crevices are bored during creation of the hole walls, material is pumped into them to form a plug which hermetically seals the area.

The entire mixing and pumping system is driven by the current generator installed on the container platform. An independently-functioning operation is therefore guaranteed. In order to be able to operate the system while protected from climatic influences, the entire control unit was installed in a suitably equipped 20 ft office container. Provision of another, equal-sized container for the transport and storage of 300 m of delivery line (pipes, hoses and couplings) completes the mixing and pumping system.

Safeguards will be effective also in future

The successful development and implementation of a mobile – and therefore suitable for use in open pits – compact mixing and pumping system was due to the connection of various components to the core of a Putzmeister KOS high density solids pump. By pumping of a mixture of fly ash, binder and water to the specific areas, further spreading of the subsurface layer fires is reduced and specific destruction of the remaining deposits is achieved. Furthermore, you are saving time by tapping new nearby brown coal deposit resources and thus guaranteeing in the long term a continuous power supply and workplaces in the region.


Ill. 1482-1
In Kosovo subsurface deposit fires are almost close to the power plants.

Ill. 1482-2
As son as oxygen is “pumped” into the layers due to fluctuations in air pressure, the brown coal deposits start burning and fire continues.

Ill. 1482-3
Glowing residue of brown coal.

Ill. 1482-4
For extinguishing subsurface deposit fire a Putzmeister high density solids pump of type KOS conveys a material of fly ash, binder and water. Some times its consistency is quite stiff.

Ill. 1482-5
Using containers the Putzmeister plant for mixing and pumping becomes mobile. The background shows the material collection container as a temporary silo with trough chain conveyor, a container platform (20 ft) with installed KOS high-density solids piston pump including and electric and hydrauklic packs as well as an office container (20 ft)

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