Combustion technology and emission reduction

Emission reduction for biomass combustion systems

The discussions about limit values for NOx and particulate matter as well as the legal requirements for combustion plants highlight the need for action to improve emission reduction for biomass plants. This poses major challenges for manufacturers and operators of biomass combustion plants. 

Our aim is to develop combustion systems with extremely low emissions (near zero emissions), even for challenging input materials. Our development work is aimed at a highly effective combination of primary and secondary measures, e.g. variable adjustment of the fuel supply with simultaneous optimized design of flue gas cleaning and filter technology.

For the scientific evaluation and subsequent optimization of the emission behavior of combustion and filter systems, test benches and measuring equipment are available in our pilot plants, e.g. online gas analysis, measurement of fine dust and nanoparticles, analysis of combustion residues, etc. The results can be used to draw conclusions. The results can be used to draw conclusions about the system integration, feasibility, economic efficiency and ecology of combustion processes and systems.

Fuel staging as an innovative process for NOx reduction

In contrast to other primary measures (air staging, recirculation of exhaust gas), significantly lower emissions can be achieved with fuel staging. One approach for this is the staging of biogenic residual and waste materials (primary fuel) with natural gas or other gaseous secondary fuels. Compared to secondary measures (SNCR, SCR), this also improves energy efficiency, as the reducing agent contributes to energy generation. In addition to reducing nitrogen oxide emissions, dynamic burner operation also increases the flexibility of energy supply. The principle of fuel staging is expected to reduce NOx emissions by at least 50 percent. 

Decentralized plants for the energetic use of biomass, e.g. biomass power plants, biomass cogeneration plants, biogas plants or firing systems for the recycling of residual materials often do not exploit all efficiency potentials. In future, digital process monitoring will enable the efficient use of varying fuel qualities in biomass furnaces. This involves combining and testing control and regulation technology with digital modules from fuel storage and fuel detection to the combustion process.

So far, however, such technologies have only been available in large biomass cogeneration plants or waste incineration plants, mainly for cost reasons. The research focus on the digitalization of biomass furnaces aims to make this possible for furnaces on a smaller scale.

Automated adjustment of the firing system to the fuel   

Although most combustion systems can process low-grade fuels such as forest residues or biogenic residues, the combustion parameters, such as the fuel supply or ventilation, must be set manually in order to ensure a stable combustion process with high burnout quality and efficiency. This manual adjustment is time-consuming, requires a lot of experience and is sometimes only possible to a limited extent. Operating errors can lead to higher emissions, wear and tear and downtime. 

Continuous digital process monitoring of the sensor, control and regulation technology is the basis for making these settings automatically in the future. This will enable economically and ecologically optimal combustion at all times.

In oxyfuel combustion, gases from the use of biomass for energy are burned with pure oxygen (O₂) instead of air. This produces only CO₂ and H₂O as combustion products in the exhaust gas. The water vapor (H₂O) condenses and the heat released can be used. The remaining exhaust gas with a CO₂ concentration of over 95 percent can be used industrially as an alternative carbon source. This enables decentralized process routes for the use (BECCU or Bio-CCU) or storage (BECCS or Bio-CCS) of CO₂.

The oxyfuel process is flexible in terms of the quality of the gaseous fuels. In addition to biogas, sewage gas, pyrolysis gas or synthesis gas can be used.

At Fraunhofer UMSICHT's Sulzbach-Rosenberg site, an oxyfuel burner system with a thermal output of 50 kW is being operated on a demonstration scale. The decentralized application of such a system can enable small and medium-sized companies in the bioenergy sector to implement CO₂-neutral or CO₂-negative process routes. 

Oxyfuel combustion processes could also become increasingly important, as considerable quantities of oxygen (O₂) will also be produced in the future if the hydrogen economy is expanded. In the electrolysis process, eight times the amount of O₂ is produced per unit of hydrogen. According to the Federal Ministry for Economic Affairs and Climate Protection (BMWK), electrolysis capacities are to be gradually expanded by 2050. As a result, around 1.8 million tons of oxygen would be produced in 2030 and up to 18 million tons of oxygen in 2050 as a previously unused by-product. Particularly at locations where bioenergy and electrolysis capacities are located together, oxyfuel processes could create an economical utilization option for the O₂.