The process gas to be analyzed is sampled by the gas sampling probe, purified in the electrically heated dust filter, and then applied to the gas analyzer. Because the opening is positioned at the side, only a part of the gas flow which has a particularly low dust concentration is sampled.
To reduce the load on the gas cooler in the analyzer cabinet, a condensation trap is present on the valve manifold. During purging of the sampling equipment, the resulting condensation is discharged from the tank.
During operation in an environment up to 1 400 °C, the probe is cooled by a heat exchanger operating at atmospheric pressure. An electronic control valve provides short heating-up times following initial insertion of the probe, and controls the temperature of the coolant in the cooling circuit.
Comprehensive monitoring mechanisms protect the probe from thermal overloading. In the event of a malfunction, the probe is automatically removed from the rotary kiln by the retraction unit.
The harsh environmental conditions at the intake of the rotary kiln result in extreme loads on the sampling probe. The process gas temperature can be up to 1 400 °C, and the dust load up to 2 000 g/m3. Caked-on materials falling down from the kiln lining present a danger for the probe through mechanical overloading.
Depending on the raw material and the fuels used, an increasing amount of sulfur, alkali and chlorides can be expected in the flue gas, which in turn may result in caking of material on the probe jacket and the production of corrosive acids.
To achieve as high an availability as possible with a minimum amount of maintenance effort, the mounting location for the probe must be determined exactly. If you are not sure about the most favorable installation location, obtain support from the supplier.
Many problems frequently encountered when using a gas sampling function in a rotary kiln can be largely avoided using the FLK probe. As a result of the high gas sampling temperature of up to 200 °C, problems associated with caking on the probe jacket and blocking of the gas paths by condensation are significantly reduced compared to water-cooled sampling systems which only achieve a gas sampling temperature of approx. 90 °C.
Cleaning of the gas sampling equipment is carried out at regular intervals using pulsed compressed air. Prior to starting the backflushing, the gas path to the gas analyzer is closed by means of a four-way ball valve. As a result of the self-cleaning effect during the rotation, the ball valve has significant advantages compared to a standard solenoid valve.
The cleaning cycle is executed in several steps:
- Cleaning of filter pipe in dust filter
- Cleaning of filter housing and probe
- Blowing of dust back into the rotary kiln.
A pressure switch in the compressed air valve manifold detects imminent blockages in the gas paths between the planned purging times, and initiates immediate purging by means of the control unit.
The quantity and hardness of the caking on the probe jacket can be extremely different with different types of rotary kiln. In addition to possible mechanical overloading of the probe, the temperature of the sampled flue gas drops as a result of the thermal insulation from the hot process gases. This results in condensation of the flue gas in the probe's sampling tube. If a temperature of 130 °C is fallen below, the sample gas pump in the analyzer cabinet is switched off as protection against the production of condensation. Caking must therefore be removed regularly.
In order to remove caking, the probe can be automatically retracted from the rotary kiln at regular intervals, initiated by the control unit of the sampling equipment and depending on the amount of caking. Caking is usually removed automatically from the probe jacket as a result of cooling down in the cold ambient air. When retracting and inserting the probe, cleaning of the probe jacket is supported by passing compressed air through nozzles in the kiln connection tube. In unfavorable cases, manual cleaning by the maintenance personnel may be necessary.
The numerous control and monitoring functions are made possible by the PLC.
Adaptation of the control parameters - such as purging frequency and duration - can be carried out at any time using the integrated operator panel.