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Heat from pit water in Bochum-Werne

EnEff:Wärme - Forschung für energieeffiziente Wärme- und Kältenetze
Arnold mineshaft at the Robert Müser colliery

Arnold mineshaft at the Robert Müser colliery

© Stadtwerke Bochum GmbH

Settlement summary

Project status Projektstatus: Phase 3Realisation
Location of network Bochum-Werne
Location of local community Bochum, 44894 Bochum, Bochum, Nordrhein-Westfalen
Settlement in figures Area: 145,46 km²; Inhabitants: 374.737
Developer, organizer Stadtwerke Bochum GmbH
Network operator Stadtwerke Bochum GmbH
Generation Gas absorption heat pumps, gas motor heat pump, electric heat pump, peak-load natural gas boiler
Heating system Before: Gas-fired boiler (natural gas); Afterwards: Gas absorption heat pump (pit water, natural gas); gas motor heat pump pit water, natural gas); electric heat pump (pit water, electricity); peak load cover, natural gas boiler, (natural gas)
Network length Cold local heating line: 0.815 km; Warm local heating line: 0.13 km km
Heat customer, cooling energy customer City of Bochum
Project themes

Project description


At the Robert Müser industrial site in Bochum, the RAG AG company extracts around 10 million m³ of pit water every year from the Arnold mineshaft and pumps it into the nearby ponds. The main aim of the project is to utilise the pit water as an energy source for providing heat. Two schools and the headquarters of the Bochum Fire Brigade Service are located close to the Arnold mineshaft. Combined together with heat pump systems, the pit water shall be used as an energy source for heating these existing buildings.


In order to reduce climate change to a minimum, the German federal government has launched its "Integrated Energy and Climate Programme". By utilising the heat from the pit water, this pilot project will already enable the annual fuel requirement for the aforementioned buildings to be reduced by approximately 1,200 MWh. That corresponds to an annual CO2 reduction of around 245 tonnes p.a.

However, the existing heat potential in the pit water will also enable much greater savings in terms of CO2 emissions to be made in future. The pit water at this location could be used as a heat source for several heat pump systems, which, depending on the models used, could have a total heat output of up to 4.5 MW. Since the development area at the former Robert Müser colliery is planned to be developed in the medium term as a commercial and industrial site, it can be assumed that there will be other buildings that will need to be supplied. The project also intends to enable the utilisation of pit water heat at other locations in the Ruhr region, where another 90 million m³ are extracted each year.

The scope of the planning encompasses the extraction of heat from the pit water, the construction of the "cold" and "warm" local heating network and the development of heat pump systems for the buildings to be connected. The local municipal utility company, Stadtwerke Bochum GmbH, was responsible for planning the “cold” and “warm” local heating network, while an external planning office was in charge of designing the heat extraction and the heat pump systems.

Concept, planning

The aim of the project is to achieve an optimally harmonised overall system, whereby the heat extraction from the pit water represents an important component of the overall system. As part of the planning, various alternatives for extracting the heat from the pit water were therefore examined in terms of both their technical feasibility – including their ability to be transferred to further projects – and their economic viability. A particular challenge is provided by the aggressive chemical composition of the pit water, which places particular demands on the choice of material for the heat exchangers. In addition, the pit water is polluted and also partly contains larger particles in suspension. These circumstances were examined in detail during the planning stage with a view to incorporating the heat exchangers and the associated hydraulic switching. Since the extraction of heat from pit water has not yet been attempted via heat exchangers, this poses a particular risk in terms of realising the overall project. For this reason, various special structures for extracting the heat from the pit water were therefore examined along with various heat exchanger systems (plate heat exchangers, spiral heat exchangers and shell-and-tube heat exchangers). The requirements for the hydraulic switching were also included in the investigation.

In general, new buildings are heated with heat pumps. In this project, however, it is planned to heat existing buildings with the heat pump technology. The heating plants were therefore correspondingly examined in detail and the requirements for the individual buildings measured. A particular challenge lay in the choice of heat generator for utilising the pit water heat supplied via the cold local heating network. Here the use of electric heat pumps and gas absorption heat pumps were investigated. Although the latter technology is not widely used in the market, in primary energy terms it offers considerable advantages. As a result of the varying situations and amounts of heat consumed in the existing buildings, different types of heat pumps are being deployed in the buildings. The direct comparison of the technical versions will enable the efficiency of the various types of heat pumps to be determined when installed in existing buildings.

The new heat generators (heat pumps) shall be used in combination with the existing, old heat generators (gas boilers for supplying peak loads and securing supplies), whereby the hydraulic connections will need to be individually optimised. In order to ensure a highly efficient operation, the heat consumers need to be divided according to high- and low-temperature use. This also required measurements to be made and the planning of sensibly optimised heating circuits. The new heat generation systems are being sized using Sochinsky’s Annual Load Duration Curve. The aim is to meet a substantial part of the annual heating requirement (at least 80%) using heat pump systems that are as small as possible.

It is already planned to use the heat from the extracted pit water in the buildings in spring 2012. This will be followed by a 4-year phase of intensive support to monitor, optimise and assess the project.


The planning costs for the pilot project are being borne by Stadtwerke Bochum GmbH. The construction and commissioning and operation phases are being fifty per cent funded by the German Federal Ministry of Economics and Technology (BMWi) as part of its EnEff:Wärme research initiative.


The planning phase was successfully concluded at the end of 2011. The project is currently in the implementation phase and the commissioning is earmarked for April 2012.

Energy characteristics

before potential after unit
Annual heating requirements of the buildings (heat generation)     3.029.000,00 kWh/a
Connected load (thermal capacity)     1.600,00 kW
Capacity of the heat pumps     690,00 kW

Cost-effectiveness characteristics

before after unit
Redesign of the heating centres and construction of the heat extraction system   850.000,00 Euro
Local heating network   270.000,00 Euro
Measurement and control technology   180.000,00 Euro

Sustainability characteristics

before after unit
CO2 reduction   245,00 t/a
  • BINE projektinfo publication "Thermal heat from pit water"