Morahalom is a small town (pop. 5800) situated in the south of Hungary on the border with Serbia. It used to be listed among the 50 most disadvantaged communities of Hungary, but the investments of the past decade - upon some the current project also builds on - launched it into the top 10 most dynamically developing settlements. The installation of the geothermal district heating system can be considered the most influential and of highest impact of them all, which also presented a solid foundation to the local GEOCOM components. It is worth noting that there are two separate geothermal heating systems in place in the town. One of them was developed solely for balneological use at the local spa, the already mentioned district heating system has a much wider impact on the community. Some key specifications of this latter have to be highlighted.
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The doublet configuration of one abstraction well (B-45) and one injection well (B-46) (1270m and 900 m respectively) allows the sustainable resource management of the 63°C thermal water produced on site from the Upper Pannonian sandstone reservoir with flow rates in the range of 25-30m3/hour in summer and 60m3/hour in winter. The annual thermal water production on this system is around 190.000m3. The full loop runs a total of 3,054 kms between the two wells serving with heat and domestic hot water (DHW) a total number of 12 municipal-owned public buildings mainly in the downtown area. By having the geothermal cascade system in place the proportion of renewable energy within the energy mix of public institutions has grown from 0% up to more than 80% - offsetting the use of 542.029 m3 natural gas annually, while providing 18.700GJ of heat per year. As a direct result annual heating-related emissions have also been reduced significantly (by 1590t of CO2, 585kg of NxOx and 1113kg of CO). The GEOCOM project aimed to improve the cascade system with a set of new elements to ensure total utilisation of geothermal energy and to demonstrate cutting edge energy efficiency/retrofitting measures that are currently lacking from geothermal projects in Eastern-Central Europe.
Thermal waters of the Morahalom region (and in a broader context, the south of Hungary) can be described by their rather high inherent dissolved gas content (average 520 l/m3 with 87% CH4). In other words for every 2m3 of produced thermal water we have an average of 1m3 methane (annually about 95.540m3) which was previously released to the atmosphere. Within the project there were two small-scale combined heat and power (CHP) engines (4-stroke, in-line 4-cylinder engine) installed at each of the production well sites to utilise the separated gas content of the produced fluid which equals to roughly 89.950m3 CH4/year. Read More
(Apart from the B-45 well of the cascade system there is another one (B-40) exclusively serving the local spa, with no feed to the district heating system and its water is not re-injected either, nevertheless it also benefits from this novel gas separation and utilisation technology). The following aspects were taken into consideration when the equipment was devised and installed: 1) To make the associated gas of the produced thermal water with 65-98 % CH4 content suitable for a continuous, operation-safe, temperature-independent communal combustion or for electric and thermal energy production with gas engine based CHP units; 2) To ensure effective, pressure controlled dew-point adjustment of the produced gas to avoid hydrate formation in the pipes and conduits; 3) To cease the atmospheric discharge of CH4 while meeting rigorous EU emission standards; and 4) To set up an automated system with no supervision to intervene in case of system malfunctions or failures.
In standard operating conditions, the technological process is automatically controlled, though the gas preparation can also be operated manually during start-up. The thermal water is pumped from the reservoir and into the production pipe as a single phase fluid until it reaches the bubble point, where the separation of the dissolved gas begins. The gas is carried on by a pressure booster from the degassing container through the dew-point adjustment cooler and the drip catcher into the gas engine. From the lower part of the drip catcher, the water condensed from the gas exits through the dedicated discharge line. From the drip-catcher, the gas reaches the CHP engine through the inlet end fitting and the adjustment valve, where it burns as the fuel of the engine. The electric power generated in the CHP unit reaches the consumers through the outlet fitting. The thermal output is transferred in the form of hot water with a temperature of 90-120 °C. It is produced by the heat exchangers of the CHP units with additional input from the cooling of the smoke gas and it is charged into the district heating system by pumps and - in case of the stand-alone application at the spa - through a secondary circuit into the spa’s domestic hot water production system.
The gas preparation system and the CHP unit are separately controlled. Both devices have a standard gas concentration and fire protection system in place and equipped with a number of safety features such as the inlet gas pressure adjuster and the automatic emergency shutdown protocol in case of malfunction to ensure safe operation.
Schematics of the waste gas utilization setup at the B-45 site
According to gas sample analyses and technical feasibility studies prior the implementation of the project, 2-2.5 kW electric energy and 6-7 kW thermal energy was estimated that can be produced in the CHP units from 1 m3 of separated gas. Now having both CHP engines up and running it can be concluded that the average power output of the unit installed on the B-45 well is 2,73 kW/m3 whilst the thermal yield is 4,366 kW/m3 with a total efficiency of 84% (34%el + 50%th). The total output of this engine is 116kW (50kWel + 66kWth). These values for the other CHP unit at the B-40 well in the spa are 2,456kW/m3 electric and 7,008kW/m3 thermal output with the same efficiency, but slightly less total output (90kW). The generated power is partly used on-site to run the pumps and other equipment while the rest is fed to the grid. The thermal output of the B-45 engine is transferred to the circulating thermal water which gains around 2°C as a result, which roughly matches the heat loss over the total length of the pipeline. At the spa the extra thermal output supports the in-situ DHW supply system. Utilising this trapped gas not only negates inefficiencies such as the heat loss over the full geothermal cascade system but burning methane instead of releasing it reduces the carbon footprint of the whole operation given that the comparative impact of CH4 on climate change is over 20 times greater than CO2 over a 100-year period. In addition the excellent combustibility of methane allows a smoother burning and lower maximum burning pressure compared to other gases which translate a reduced load on the various engine parts ensuring a much longer lifetime.