Emission Limited Biomass Combustion

In plant operation, the larger the plant, the greater the demands on combustion control due to fuel variability. For small boilers, lambda probes (zirconium oxide probes) are state of the art. In medium-sized and larger plants, however, lambda probe control is no guarantee for low-emission combustion due to fuel inhomogeneity and variation.   The project EmiL (Emission Limited Biomass Combustion) is working on the foundation research to create the basis for highly efficient and low-emission biomass boilers.

The project results are being developed in close cooperation between research institutions, universities and boiler manufacturers. The industrial research project addresses medium-sized biomass boiler plants with a capacity range between 50 kW and 1.0 MW.

Methodology

The goal of low-emission biomass combustion is achieved through a combination of primary measures in the area of combustion sensor technology and combustion control, as well as secondary measures in the area of cost-efficient particulate matter separation technology. An integrated research approach optimises these sub-areas to create a holistic solution. The methodology is based on experimental investigations on test benches and in real plant operation. An innovative model predictive control system is being developed, which is being experimentally investigated by implementing it in a LabVIEW® environment via an interface to the boiler control system. In the field of particulate matter separation, the integration of particulate matter separators into the boiler unit is being tested on the basis of CFD simulations and experimental investigations on a test rig.

Results

The focus is on the development and testing of model predictive control (MPC), which enables the use of a wide variety of biogenic fuels while minimising pollutant emissions through adaptive parameterisation. This is supplemented by the integration of combined sensors that can detect trace gases such as CO and NOx in addition to the flue gas oxygen content.

Another focus is on the direct integration of electrostatic precipitators into biomass boilers. Compared to external separation systems, this technique for reducing particulate matter offers advantages in terms of cost, space requirements and controllability. Experimental investigations can demonstrate the technical feasibility and create the scientific basis for subsequent product development.

The results of the project include:

• a validated, emission-limiting MPC control system for 100 kW biomass boiler systems
• new findings on the accuracy, cross-sensitivity and ageing of combined exhaust gas sensors
• the successful integration and testing of an electrostatic precipitator in biomass boilers
• a comprehensive understanding of emission behaviour under variable operating conditions and fuels

The project EmiL makes an essential contribution to the low-emission, efficient and flexible use of biogenic solid fuels – a key factor for the future role of biomass in a sustainable energy system.