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 within a few years. 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. 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 Heilbronn’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 Heilbronn 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. Among others, the existing coal power plant block currently performs this role. Only by building a large CCGT plant will it be possible to decommission coal block HLB7 without endangering the security of the power supply.

Direct conversion of a plant that supplies power to an urban area such as Heilbronn 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 Heilbronn’s district heating network were to be operated with hydrogen produced regionally from wind power, 150 additional wind turbines would have to be built in the area surrounding Heilbronn. 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 still in the early planning phase, with the approval process divided into two parts. The city of Heilbronn will initiate the process for the necessary adaptation of the development plan for the power plant site in September. In the course of 2022, we will then prepare the approval process at EnBW in accordance with the Federal Immission Control Act (BImSchG). It is likely that the application for this can be submitted to Stuttgart Regional Council in the first half of 2023. Assuming approval is granted and a final investment decision is taken, construction of the new plant could begin in the last quarter of 2023. The new plant could then be commissioned sometime in 2026.

Detailed information on the project’s approval process overseen by the city of Heilbronn can also be found on the website for the city of Heilbronn.

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 ancillary facilities will be newly constructed in the area to the east of the cooling tower. In addition, it is planned to build a district heating storage facility, which will also be located in the area to the east of the cooling tower.

Once the new Block 8 has been commissioned, Block 7 at the Heilbronn site can be shut down. As soon as it is also possible to remove Blocks 5 and 6 from the grid with the approval of the Federal Network Agency, 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.

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 city of Heilbronn.

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, Block 7 will be shut down in addition to Blocks 5 and 6. Just a few of the major components – such as auxiliary steam generator 3, the 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. For Heilbronn, in concrete terms, this means that the new CCGT plant can cut carbon emissions by over one million metric tons per year, reducing the figure to around 50 percent of the current emissions at the coal power plant. The climate in the city also benefits directly: Emissions of nitrogen oxides (NOx) would be cut by about 80 percent compared to the current figure, while those of sulfur oxides (SOx) would drop by more than 90 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 Heilbronn and the surrounding region are reliably guaranteed at all times.

When the district heating network was built in Heilbronn, power plant technology at the time made it common practice to draw off steam from the power plant process and use it as a heat transfer medium for district heating. From today’s perspective, however, steam networks have various disadvantages: They diminish the efficiency of modern power plant technology, while heat losses are higher and maintenance and repair work is more complex than with a district heating network based on hot water. The advantage of a steam district heating network is the high temperature of over 100°C. Yet 95 percent of all district heating customers only need heating at a temperature level below 100°C. Overall, the advantages of a hot water district heating network outweigh those of a steam network: The improved power plant process can increase the electricity yield in the power plant – benefiting the environment, because fewer carbon emissions are produced. The maintenance costs in the district heating network will fall – a plus for customers. The conversion can be carried out with little impact on customer supply and the cityscape.

Throughout the project, EnBW will keep people regularly updated on its progress and report on milestones on the website www.enbw.com/heilbronn.

On 30 July 2021, an online information event took place, during which the project was presented to citizens. Interested parties were able to put questions live to those present in the studio at the Harmonie Concert and Congress Center in Heilbronn.

In addition, information tours in small groups were held in October on the power plant site in Heilbronn, during which interested parties could find out more about the project. Further tours are currently being planned. There will be announcements in good time both on the project website and via advertisements informing people how they can attend.

However, you can always send any questions, suggestions or criticism by e-mail to

heilbronn@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).