From coal to natural gas to hydrogen

The goal of climate neutrality is neither achievable for individual companies nor entire states in a single step. With regard to heat generation in particular, renewable energies are not yet in a position to fully replace fossil fuels in the short term. Replacing coal with natural gas is therefore a sensible intermediate step because it can roughly halve greenhouse gas emissions compared to coal in the short term and therefore significantly reduces carbon emissions.

This is especially the case when indirect emissions generated by mining and transport are taken into account. That’s because the fuel switch also avoids indirect emissions associated with coal mining and transport, such as emissions of mine gas, which has a high methane content. The nice thing is that a natural gas power plant does not stand in the way of the ongoing journey toward climate neutrality. The gas turbines used are very flexible and can be converted to burn “green gases” in the future, including hydrogen, which is produced by means of electrolysis using electricity from renewable energy sources.

Accordingly, the switch to natural gas represents a bridge on the way to green gases, with which complete climate neutrality can then be achieved by 2035.

When a fuel is used to generate energy, then it is essential for environmental and climate change mitigation reasons that this fuel is used as efficiently as possible – in other words, as much usable energy as possible is generated in the form of electricity and heat from a given amount of fuel. With a so-called combined cycle gas turbine (CCGT) plant, the best use by far can be made of the fuel, while simultaneously generating electricity and heat (known as combined heat and power, or CHP for short.

Put simply, a CCGT plant consists of a gas turbine, a steam turbine and heat exchangers for the production of hot water. In this way, the heat produced during the combustion of natural gas is used three times in a row. First of all, the hot combustion gases drive the gas turbine, which then produces electricity using a generator. The flue gases flowing out of the gas turbine are still so hot that water can be evaporated in a so-called waste heat boiler. The resulting steam is then used to drive a steam turbine, which again produces electricity using a second generator. After driving the steam turbine, the steam condenses back into water, which still has a temperature of around 100° Celsius. This residual energy is delivered as useful heat to the town’s district heating system, supplying private households as well as commercial and industrial businesses. As a result of this three-stage system, a modern CCGT plant can achieve a fuel utilization efficiency rate of over 80 percent, significantly helping to cut carbon emissions by around 50 percent compared to the current coal power plant. No other technology can help to cut carbon emissions to this extent in such a short space of time.

The fact that the CCGT plant planned in Altbach/Deizisau will have a comparatively high electrical output of up to 750 MW is due to the electricity demand in the region. Ultimately, if renewable energy from wind power and photovoltaics is not available, controllable power plants must be able to meet this electricity demand. Existing coal power plant blocks, among others, currently perform this role. Only by building a large CCGT plant will it be possible to decommission coal blocks HKW 1 and HKW 2 without endangering the security of the power supply.

Direct conversion of a plant that supplies power to urban areas such as Stuttgart or Esslingen to run on regional renewable energy sources is almost unfeasible. This is because renewables require a lot of space due to their low energy density. In addition, the most powerful renewable energy sources – wind power and photovoltaics – are not controllable. They only supply their energy when the natural resource – wind or sun – is available and not necessarily when there is demand for electricity and heat. For this reason, renewable energy sources must be made storable and then stored – through the production and storage of biogenic gases, for example.

The following example highlights the kind of Herculean task we are talking about here: If Stuttgart’s district heating network were to be operated with hydrogen produced regionally from wind power, 250 additional wind turbines would have to be built in the area surrounding Stuttgart. To put this figure into context, just 13 new wind turbines were built in the whole of Baden-Württemberg in 2020. Electrolyzers and storage systems would also need to be built. It thus quickly becomes apparent that such a conversion would not only take decades, but also make the price of district heating much more expensive. Rough estimates show that the production costs for district heating would more or less quadruple in such a system. A significant increase in energy prices, however, would threaten broad acceptance and thus the success of the energy transition itself. The intermediate step via natural gas therefore not only leads to a significantly faster reduction in greenhouse gas emissions by around 50%, but also gives renewable energy sources the time needed to manage the required growth and exploit the potential for cost-efficient hydrogen production. At the end of this development, the new CCGT plant will also be operated with hydrogen produced from renewable sources and will therefore be climate-neutral.

If work begins at the end of 2023, we expect the new building to be completed in mid-2026.

The project is currently in the planning phase. In the course of 2022, we will then prepare the approval process at EnBW in accordance with the Federal Immission Control Act (BImSchG). The application for this is expected to be submitted to Stuttgart Regional Council by the end of 2022. Assuming approval is granted and a final investment decision is taken, construction of the new plant could begin in the third quarter of 2023. The new plant could then be commissioned sometime in 2026. There is also early public involvement in the approval process. We organized matters in this regard at the end of October 2021 with an information event on the new construction measures.

EnBW currently estimates the potential investment figure to be over EUR 500 million. However, the company’s final investment decision can only be taken upon completion of the approval process.

The CCGT plant with auxiliary facilities will be built in the area south of the HKW 1 cooling tower. It is important to mention that the hybrid cooling tower belonging to coal block HKW 1 is also set to be used for the new CCGT plant. The water treatment facilities will also be upgraded and remain in operation. The planned hot water boiler plant will be built in the existing district heating building belonging to HKW 1.

Once the new Block 3 has been commissioned, HKW 1 and HKW 2 at the Altbach/Deizisau site can be shut down. As soon as the new CCGT plant has commenced safe commercial operations, the coal dump can be taken out of operation. A decision is yet to be taken as to how the areas will be used in the future. The western section of the coal dump is needed for the construction of the new CCGT plant anyway.

Unfortunately, the noticeable presence of the construction measures in the area is unavoidable. However, EnBW will endeavor to keep the impact to a minimum and remain in dialog with local residents.

Construction work will mostly take place during the day, with heavy loads being transported at night wherever possible. All construction measures will be carried out as per the approval process in close consultation with Stuttgart Regional Council and the affected municipalities in the surrounding area.

Various expert reports need to be commissioned as part of the approval process, which also consider any impact on the residents. Among other things, sound reports and air pollutant immission forecasts are compiled, which consider the impact of the new building on the surrounding area and the environment:

• Noise control: Once the new plant has been commissioned, blocks HKW 1 and HKW 2 will be shut down. The gas turbine plants as well as the HKW 1 cooling tower and the water treatment plant will remain in operation even after the new plant has been commissioned. The decommissioned plants contribute significantly to the current noise emissions on the site. The new plant will be equipped with state-of-the-art sound absorbers, sound traps, etc. in order to stay within legal limits as specified in noise control guidelines (TA Lärm). In addition, there will no longer be any disposal of residues or delivery of additives associated with the flue gas cleaning system at the coal plants, which will in turn reduce the volume of traffic and the resulting noise.
• Water pollution control: Among other things, the decommissioning of the old plants and the commissioning of the new plants will result in significantly less heat being introduced into the Neckar in the future. This will improve the water pollution control situation compared to the status quo.
• Immission control: Switching from coal to natural gas will significantly reduce emissions of carbon dioxide (CO2) and other substances that have an impact on the climate. In concrete terms, this means that the new CCGT plant can cut carbon emissions by over two million metric tons per year, reducing the figure to around 40 percent of the current emissions at the coal power plant. The climate in the town also benefits directly: Emissions of nitrogen oxides (NOx) would be cut by about 25 percent compared to the status quo, while those of sulfur oxides (SOx) would drop by more than 75 percent.

Until all new power plant and district heating facilities have been fully commissioned, the coal boilers will remain available for supplying electricity and district heating. By taking this approach, we will ensure that supplies in Altbach, Deizisau and the surrounding region are reliably guaranteed at all times.

No – as in the case of the fuel switch project already implemented at the Stuttgart-Gaisburg site and the fuel switch at the Stuttgart-Münster site, the district heating supply is assured at all times. Before blocks HKW 1 and HKW 2 are finally decommissioned, a replacement plant for the district heating supply will be built in addition to the CCGT plant. This will be ready much earlier than the new CCGT plant and will ensure a secure supply of district heating even in times when the CCGT plant is not in operation. In addition, the linking of the “Mittlere Neckar Line” will also makes it possible to supply the district of Esslingen with heat from the power plants located in the Stuttgart area.

Throughout the project, EnBW will keep people regularly updated on its progress and report on milestones on the website www.enbw.com/altbach-deizisau. On 26 October 2021, an online information event took place, during which the project was presented to citizens. People who took part were able to put questions live to those present in the studio.

However, you can always send any questions, suggestions or criticism by e-mail to altbach-deizisau@enbw.com.

The project falls under Number 1.1 of Annex 1 of the Fourth Regulation on the Implementation of the Federal Immission Control Act (Regulation on Plants Requiring Approval, 4th BImSchV). Pursuant to Annex 1 Number 1.1.1 Column 1 in conjunction with Section 3b of the Environmental Impact Assessment Act (UVPG), there is a duty to carry out an environmental impact assessment. The environmental impact assessment is an integral part of the approval process pursuant to BImSchG (Section 1 Paragraph 2 of the Regulation on the Approval Process (9th BImSchV)) and is conducted by Stuttgart Regional Council as the competent approval authority.

Approval of the project should grant a full permit for the construction and operation of the plant pursuant to BImSchG and environmental law as well as the release of greenhouse gases (carbon dioxide) pursuant to the Greenhouse Gas Emissions Trading Act (TEHG).