• Energy Research

Hydrogen as a carbon-free fuel is commonly expected to play a major role in future energy supply, e.g., as an admixture gas in natural gas grids. Which impacts on residential and commercial gas appliances can be expected due to the significantly different physical and chemical properties of hydrogen-enriched natural gas? This paper analyses and discusses blends of hydrogen and natural gas from the perspective of combustion science. The admixture of hydrogen into natural gas changes the properties of the fuel gas. Depending on the combustion system, burner design and other boundary conditions, these changes may cause higher combustion temperatures and laminar combustion velocities, while changing flame positions and shapes are also to be expected. For appliances that are designed for natural gas, these effects may cause risk of flashback, reduced operational safety, material deterioration, higher nitrogen oxides emissions (NOx), and efficiency losses. Theoretical considerations and first measurements indicate that the effects of hydrogen admixture on combustion temperatures and the laminar combustion velocities are often largely mitigated by a shift towards higher air excess ratios in the absence of combustion control systems, but also that common combustion control technologies may be unable to react properly to the presence of hydrogen in the fuel.

Abstract In many energy-intensive manufacturing processes, natural gas is the dominant fuel to provide process heat. There is increasing pressure, however, to reduce both fuel costs and carbon dioxide (CO2) emissions. One possible approach in this regard is the use of mostly untreated biogas as a fuel in a co-firing approach. While the use of such biogas can decrease both natural gas consumption and overall CO2 emissions (biogas is considered to be a CO2-neutral fuel), there is concern how this change of fuel will impact on product quality, combustion behavior and the refractory material. Trace contaminations in the biogas are one aspect in this context which might have a negative impact on product quality or the durability of the refractory of industrial furnaces. In a previous research project, GWI and its partners investigated the principal applicability of biogas combustion, using the glass melting process as an example. It was found that there was no negative impact on combustion behavior, product quality or refractory properties if the process is adapted to the different characteristics of the fuel, for example by adjusting melting times. Another result was that for existing plants, it is more sensible to use a co-firing approach, partly substituting natural gas by biogas, instead of switching fuels completely. Consequently, the co-firing of roughly de-sulphurized biogas in an industrial glass melting furnace in Germany is currently being investigated as part of a follow-up project. Aspects such as pollutant formation, energy efficiency and product quality when using untreated biogas on an industrial scale will be examined.

Abstract Operators of public electricity grids today are faced with the challenge of integrating increasing numbers of renewable and decentralized energy sources such as wind turbines and photovoltaic power plants into their grids. These sources produce electricity in a very inconstant manner due to the volatility of wind and solar power which further complicates power grid control and management. One key component that is required for modern energy infrastructures is the capacity to store large amounts of energy in an economically feasible way. One solution that is being discussed in this context is “power-to-gas”, i.e. the use of surplus electricity to produce hydrogen (or even methane with an additional methanation process) which is then injected into the public natural gas grid. The huge storage capacity of the gas grid would serve as a buffer, offering benefits with regards to sustainability and climate protection while also being cost-effective since the required infrastructure is already in place. One consequence would be, however, that the distributed natural gas could contain larger and fluctuating amounts of hydrogen. There is some uncertainty how different gas-fired applications and processes react to these changes. While there have already been several investigations for domestic appliances (generally finding that moderate amounts of H2 do not pose any safety risks, which is the primary focus of domestic gas utilization) there are still open questions concerning large-scale industrial gas utilization. Here, in addition to operational safety, factors like efficiency, pollutant emissions (NOX), process stability and of course product quality have to be taken into account. In a German research project, Gas- und Warme-Institut Essen e. V. (GWI) investigated the impact of higher and fluctuating hydrogen contents (up to 50 vol.-%, much higher than what is currently envisioned) on a variety of industrial combustion systems, using both numerical and experimental methods. The effects on operational aspects such as combustion behavior, flame monitoring and pollutant emissions were analyzed. Some results of these investigations will be presented in this contribution.

The decarbonization of industrial process heat is one of the bigger challenges of the global energy transition. Process heating accounts for about 20% of final energy demand in Germany, and the situation is similar in other industrialized nations around the globe. Process heating is indispensable in the manufacturing processes of products and materials encountered every day, ranging from food, beverages, paper and textiles, to metals, ceramics, glass and cement. At the same time, process heating is also responsible for significant greenhouse gas emissions, as it is heavily dependent on fossil fuels such as natural gas and coal. Thus, process heating needs to be decarbonized. This review article explores the challenges of decarbonizing industrial process heat and then discusses two of the most promising options, the use of electric heating technologies and the substitution of fossil fuels with low-carbon hydrogen, in more detail. Both energy carriers have their specific benefits and drawbacks that have to be considered in the context of industrial decarbonization, but also in terms of necessary energy infrastructures. The focus is on high-temperature process heat (>400 °C) in energy-intensive basic materials industries, with examples from the metal and glass industries. Given the heterogeneity of industrial process heating, both electricity and hydrogen will likely be the most prominent energy carriers for decarbonized high-temperature process heat, each with their respective advantages and disadvantages.

Abstract In recent years, natural gas quality has become a contested topic for market partners along the gas value chain, especially in the context of the European gas quality harmonization process. While a consensus could be achieved on many aspects of gas quality regulation, leading to a first European standard for H-gas quality (EN 16726), this standard lacks any regulation of combustion-related properties except for a minimum Methane Number. There is also significant uncertainty to what extent gas quality variations actually occur in German gas grids today and how they may affect gas-fired applications. This was the focus of two surveys carried out by a group of German gas-related research organizations in which gas quality measurements over long periods of time were compiled for various regions in Germany to highlight frequency and severity of local gas quality and composition changes. While one of these studies concentrated on the glass industry and also looked at possible measures to compensate for gas quality fluctuations, the other took a broader view, investigating common adjustment practices, awareness of gas quality issues among operators of gas-fired equipment and typical countermeasures by a statistical analysis of all sectors of German gas utilization (domestic, chemical and thermal processing industries, power generation). It appears likely that these findings can be transferred to other countries to a certain extent. The results of these studies as well as background information on the European gas quality harmonization process will be the focus of this contribution.

Abstract Natural gas, when compared to other solid, liquid or gaseous fuels, offers a cleaner and more environmentally friendly combustion. Nevertheless, it also produces unwanted pollutant species such as nitrogen oxides (NOx) and carbon monoxide (CO) when fired in combustors of industrial gas turbines under high temperature and pressure. These emissions of NOx and CO are harmful for human and nature and need to be kept below the regulatory limits. This problem has been the subject of numerous research and development activities for decades. The current state of the art provides well-developed firing systems for industrial gas turbines, which ensure NOx and CO emission levels well below the legal limits [1 - 5]. A comprehensive overview of the characteristics currently available gas turbines on the German market is offered by the revised version of the ASUE brochure from 2015 in [6], where beyond the reference list about industrial and municipal gas turbines, NOx reduction methods and achieved NOx emission values are recorded. Nevertheless, there still is the need for additional research in order to contribute to both the simplification of the still complicated design of the overall combustor concepts and the further reduction of harmful emissions.