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Bioenergy grid integration: Demonstrating the value of a combined heat and power district heating unit based on a wood pellet gasifier in the future energy system.
Natural gas is a widely-used form of feedstock for combined heat and power (CHP) district heating units. For gas engines, natural gas, biogas from anaerobic digestion, or wood can be used as feedstock. Whereas biogas is a renewable form of feedstock that can be used more or less directly in the gas engine, wood has to be transformed into a combustible gas via gasification.
In Rheinfelden, AEW Energie AG, an energy and heating supplier in the Canton of Aargau, is taking advantage of this fact and has contracted the company Burkhardt to build their first wood gasifier in a heat and power cogeneration unit in Switzerland based on wood pellets. The wood gasifier is a fixed bed gasifier designed to transform the fuel wood pellets into wood gas. This gas is used in a specially adapted gas engine with 180 kW electrical power. The heat produced is fed into a local heat distribution network; the electricity is fed into the local transmission grid. Such a plant makes it possible to produce renewable energy on a small scale in a combined generation of heat and power. Different from other sources of renewable energy, the unit is flexible and controllable and can therefore produce heat and electricity when there is demand.
Cogeneration with wood pellets. Source: Burkhardt (2018, March 18). V 3.90 Burkhardt wood gasifier
Monitored flue gas emission
In collaboration with researchers from the Paul Scherrer Institute (PSI), AEW Energie AG intends to monitor the flue gas emissions arising from its new CHP unit. Through gas measurements the company will be able to gather data on various types of emissions and compare this data with data from other energy production units, making sure the most optimal and efficient technology is used going forward.
Another field of interest is the specific type of wood pellets used in the unit. By using different types of wood pellets, PSI can run controlled experiments and gain a thorough understanding of the environmental impact of those types. Especially when introducing CHPs in more densely populated areas, it is crucial to understand such impact and the local emissions created with or without flue gas treatment.
Bioenergy – an internal part of the power supply system of the future
Finally, it is essential to comprehend how CHPs could fit into the future energy system and what the requirements are. Bioenergy has the potential to play a key role as a flexible resource in the renewable power supply system. While bioenergy could certainly contribute in a significant way to balancing future grids, it can also be expected that competition between different forms of flexibility will occur. Hydropower, batteries, demand side management, power to heat, etc. will be alternatives to bioenergy for balancing. It is not likely that there will be “one-solution-fits-all”, but rather different options will be used to different degrees of combination, depending on flexibility needs and local characteristics. Moreover, gas and heat networks can and should also play a bigger role in balancing the electrical grid. In all these, bioenergy can play a central role.
Historically, CHP plants are primarily operated to follow a local heat load. The role of biomass in additionally helping balance the electricity grid in general will be an important topic going forward. Due to the considerable increase of photovoltaics in the electricity system, the demand for production in the summer months could weaken considerably and hence CHPs are likely to run on a more seasonal basis. The combination of a system with CHP, heat pumps and batteries has the potential for both generation and demand-side interaction to control the energy balancing – assuming the entire combination is available – and thereby providing energy services. Those services will be the key for creating viable business cases in the future.
About the authors: Louis Lutz is the head of renewable energies at AEW Energie AG. He built this business from scratch in less than ten years, and it now consists of production units in hydro, wind, solar and biomass.
Serge Biollaz leads the SCCER BIOSWEET research area “biomethane” and is head of the Thermal Process Engineering group at the Paul Scherrer Institute.