CEM - Abstract

Abstract Information :

Climate change and reduction of CO2 emissions drives the need to replace fossil fuels, especially coal from use in power generation. This change presents known challenges for power plant operators. Power plants that fire biofuel or waste have been shown to suffer from boiler and heat exchanger surface degradation due to corrosion. This problem can be mitigated by the use of additives, co-firing of biomass and coal or lowering combustion temperature. All of these methods aim to eliminate the formation or adsorb the corrosive species. Although the use of these methods is fairly straightforward, evaluating the effectiveness has been mainly carried out by inspecting the boiler and heat exchanger surfaces after some time of operation, which makes optimization of the process slow and expensive. In this work, we present instrumentation and a method how to measure the corrosive species directly from combustion zone. In addition we will present measurement results from using this method in a modern biomass power plant. The used instrumentation can be divided into two parts, the sample conditioning system and the measurement instrumentation. The key component of the sample conditioning system is a patented high temperature probe, which allows sampling from up to 1200 degrees C. The high temperature probe operates as follows: A high temperature sample is drawn from combustion zone into the probe where it is immediately diluted and the temperature is dropped to ~200-400 degrees C in a controlled fashion. This temperature drop is similar to what happens on boiler and heat exchanger surfaces. In the high temperature probe however the corrosive species are captured in particulate form instead of depositing on surfaces. The high temperature probe is followed by the Dekati eDiluter Pro, which acts as the pump of the sample conditioning system and further dilutes the sample while dropping the sample temperature to ambient level. The diluted sample is then measured with the Dekati Electrical Low Pressure Impactor + (ELPI+) which measures the particulate concentration and size distribution from 6nm to 10µm in real time. It has been found in previous studies that if corrosive species are present, they form a distinctive nucleation mode which can be measured with the ELPI+ instrument. Subsequent chemical analysis is typically used to understand the source and nature of the corrosive species. Chemical analysis can be carried out from samples collected on the ELPI+ collection substrates or from a parallel gravimetric collection instrument. This method allows for fast tuning of process parameters with the aim to reduce the use of additives and coal in co-combustion, while increasing the combustion temperature. Therefore the overall efficiency of the plant can be increased while reducing the harmful effects of corrosion. Using this method in the modern biomass power plant showed the effect of combustion zone sampling location and power plant load on concentration and size of produced particulates.