Study on reducing emissions from vehicles in underground mining
From 1 January 2017 to 31 December 2018, the Mobile Machinery Division conducted a study on reducing diesel engine emissions from mobile machinery in underground mining, which was funded by the Baden-Württemberg Ministry of Economic Affairs, Labour and Housing. The study was carried out in collaboration with e-mobil BW and four mining companies based in Baden-Württemberg, whose operations differ in particular in terms of the type of extraction, the raw materials extracted and their size.

Study content
As part of the study, measures were developed to reduce diesel engine emissions (DME). To this end, selected haulage vehicles used in the mines were analysed in terms of their frequency, performance profile and energy consumption. Various series of measurements were carried out for these investigations in order to map the vehicles in their daily operation and to build up a representative database. In a further step, the state of the art and research into energy storage systems and emission-reduced mobile machinery was researched and documented in order to be able to generate promising measures. From this, measures were derived that can contribute to the reduction of DME underground. The electrification of mobile machines was seen as a key technology in this study, as electrified vehicles do not generate DME locally. Selected vehicles in the participating mines were analysed with regard to their electrification capability and corresponding concepts were developed. The electrification potential of the vehicles and its influencing variables were defined and determined for this purpose. Based on the results gathered in the course of the study, the research requirements that need to be met when converting a mine to emission-free extraction were then derived. Finally, the procedure used in the study was summarised in the form of a method that can be used to convert any other mine to DME-free production.

Results
As a result, the study showed that electrified alternatives are available on the market for selected vehicles, although these are lacking, especially for machines with a high payload (greater than 11 tonnes, as at 31/12/2017) or high power. Loader trucks (LHD) have proven to be particularly problematic in this regard. This is largely due to the batteries currently available on the market, whose volumetric energy density is still far too low to be used sensibly on mobile machines with high energy/power requirements. Even increased charging rates or battery replacement systems have not yet been proven to solve this problem. Although the switch from conventional (drilling and blasting) to mechanical extraction would solve the problem of the lack of electrified high-performance LHDs, there are not yet sufficient numbers of electrified dumpers for material transport on the market (as at 31 December 2017). Conveyor belts could be used as an alternative. In principle, however, the switch to mechanised extraction entails certain restrictions and immense investment costs, which makes their use uneconomical, especially in small mines. Although cable-connected machines are available in the necessary performance classes, they cannot provide the required degree of flexibility and productivity. Other drive technologies that promise zero local emissions are not yet sufficiently available on the market. The study has also identified a number of minimally invasive measures that could be implemented in the short term to alleviate the current problem situation - however, this cannot bring about a solution.

Acknowledgements
The Institute Mobile Machines would like to thank all those involved in the project for their cooperation and in particular the Ministry of Economic Affairs, Labour and Housing for their support.