## 2 Materials and Methods
### Methodology  
General operability and behaviour of the boiler when using manganese ore as bed material was studied by observations and measurements of process parameters over the course of the experimental campaign:  
* Temperature at different key locations in the boiler. Shows whether manganese ore facilitates fuel conversion in the dense bed and if less combustion takes place in the cyclone, compared to when sand is used. * Pressure drop over key components. Shows where the bed material is located in the system, whether the bed fluidizes as expected or if it has tendencies to agglomerate. It also provides an indication if there is excessive attrition of the bed material. * Amount of elutriated ash and solids captured in the secondary cyclone and the textile filter. Samples were taken each day for the purpose of elemental analysis. This allowed for setting up a fundamental mass balance over the boiler. Samples of bed material were also extracted from inside the boiler during operation. This was done using a special cooled collection probe. Extracted samples were subject to standard bed agglomeration tests at a research institute (SP Sveriges Tekniska Forskningsinstitut AB, (Boras, Sweden), in order to determine tendencies of the bed material to agglomerate at severe conditions. The methodology was as follows. A sample of 200 g was placed in a 140 cm long tube reactor with an inner diameter of 7 cm. The sample was located on a sintered metal plate allocated in the middle of the tube, which also acts as gas distributor. The sample was fluidized with 20 l\({}_{n}\)/min air, which corresponds to a superficial gas velocity of about 0.5 m/s at 750 \({}^{\circ}\)C. The pressure drop over the bed is measured with a pressure transducer and the temperature is monitored with a K-type thermocouple. The test is initiated when the bed temperature is stabilized at 750 \({}^{\circ}\)C. From this point, the bed temperature is increased by 3.5 \({}^{\circ}\)C/min. The maximum temperature was 1100 \({}^{\circ}\)C. If the bed agglomerates, the pressure drop is reduced. Three temperatures were reported:  
* T\({}_{\text{A1}}\) (first tendency towards agglomeration): This is the lowest temperature when a disturbance in the pressure drop over the bed can be verified. \begin{table}
\begin{tabular}{c c} \hline \hline
**Gas Component** & **Measuring Method** \\ \hline Methane (CH\({}_{4}\)) & NDIR, GC \\ Carbon monoxide (CO) & NDIR, GC \\ Carbon dioxide (CO\({}_{2}\)) & NDIR, GC \\ Oxygen (O\({}_{2}\)) & PMOD, GC \\ Hydrogen (H\({}_{2}\)) & GC \\ Nitrogen (N\({}_{2}\)) & GC \\ Nitric oxide (NO) & CL \\ Nitric dioxide (NO\({}_{2}\)) & CL \\ Dinitrogen oxide (N\({}_{2}\)O) & GC \\ Total hydrocarbons (THC) & FID \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Overview of measured gas components and instrumentation. NDIR = Non-Dispersive Infrared Sensor, GC = Gas Chromatography, PMOD = paramagnetic oxygen detector, CL = Chemiluminescence, FID = Flame Ionization Detector. * T\({}_{\rm A2}\) (apparent agglomeration): The lowest temperature when agglomeration clearly is taking place. The bed is considered to be agglomerating when the pressure drop is reduced continuously with 5 Pa/min or more. * T\({}_{\rm A3}\) (complete agglomeration): The temperature when the pressure drop is stabilized at its minimum value. The effect on emissions and possibility to reduce air-to-fuel ratio was studied by performing lambda experiments. These experiments basically consisted of a step-wise reduction of air-to-fuel ratio during operation and measuring the emissions. Since the research boiler is an industrial production unit operated on commercial basis, the degrees of freedom to achieve this are limited. The control system of the boiler regulates the rate of fuel feeding based on the oxygen concentration in the flue gases. Any changes here affects bed temperature. However, it is possible to regulate temperature to some extent by changing the amount of flue gas recirculated to the boiler.