*2.2. Research Stand*

The laboratory stand used in the research enables the simulation of combustion processes taking place in water boilers with a fixed grate and with a movable grate (e.g., belt grate). The diagram of the test stand shown in Figures 1 and 2 presents the view of its most important part. The main element of the stand is the combustion chamber consisting of two basic parts: the upper and the lower part. In the lower part, it is possible to regulate the heating temperature of the chamber up to 1200 ◦C. In the upper part, a water jacket is applied.

The lower part of the installation, due to the possibility of heating to a constant temperature, enables the simulation of the vault ignition (afterburning) of a grate boiler. The heated chamber walls also simulate the influence of the remaining parts of the real boiler on the combustion fuel sample. The lower part of the test installation is designed to operate at temperatures up to 1800 ◦C. The upper part of the boiler allows the exhaust gas to be cooled in a manner similar to that occurring in the upper part of the combustion chambers of water boilers.

In order to quickly load the fuel sample into the furnace chamber and to allow the fuel to be placed on the grate, the grate is placed on a movable bed. The bed is pushed inside after the lower chamber has been heated to the assumed temperature.

The combustion chamber is equipped with a number of measuring nozzles that allow for temperature measurements and gas sampling at various points. The installation is equipped with a system of devices enabling the control of the size of air stream and its measurements. Due to the above-mentioned features, the installation enables the maintenance of repeatable values of the regulated factors. In order to measure the composition of the exhaust gases, samples were taken from a stub-pipe mounted in the chimney. The stub-pipe was located near the top of the combustion chamber. The concentrations of the analyzed gases were measured using the MGA 5 analyzer by MRU GmbH (Neckarsulm Germany). The analyzer measured CO2, CO, NO, and SO2 concentrations using infrared sensors. Additionally, in the case of NO2, the analyzer was using a catalytic converter. The accuracy of the exhaust gas analyzer was ±5% of the measured value [41].

**Figure 1.** Test stand scheme: A—flue gas analyzer, S—boiler control system, W—fan, 1—rotameter, 2—valve, 3—moveable bed with grate, 4—grate, 5—surge tank (firepan), 6—rail, 7—air supply nozzle, 8—heating element (electrical), 9—water jacket, 10—discharge tunnel, 11—measurement probe, 12—probe head, 13—heated hose, 14—electric cables, 15—cooling water circulation, 16—water/air heat exchanger (cooler), 17—circulation pump, 18—surroundings.

**Figure 2.** View of the test stand: 1—lower part of the stand (heated), 2—upper part of the stand (water-cooled), 3—movable bed with a grate (inserted), 4—connection point for the primary air duct, 5—water/air heat exchanger (cooler), 6—measurement point of exhaust gas composition, 7—raised furnace closure (lowered for the heating time of the stand).
