Sludge Drying Safety Equipment

The dryer and the entire process is equipped with a multitude of safety equipment.  A Siemens S7 1500 SPC control unit checks, controls and monitors the entire drying process.  If the sensor technology recognizes deviation, the process is adjusted.  In case of faults, the automatic control unit takes suitable measures and switches off the entire drying operation. 

  • Exhaust System

On the exhaust pipe over the sound absorber, a t-piece is fitted with a dual action exhaust gas valve.  A mechanically fixed connecting rod ensures that the required exhaust gas path is free or closed, as applicable.  While the valve closes in one direction, the other vale opens at the same time.  Irrespective of the drying process, the CHP continues to function unhindered.  The drive unit of the valve is secured in a failsafe function.  This means that if the control signal fails, the power cuts out or there is a sudden drop in pressure, the exhaust gas path to the dryer will be immediately closed by means of a mechanical or battery-operated spring reset.  The exhaust gases are discharged via the exhaust gas pipe of the CHP. 

  • Temperature Monitoring

Temperature sensors are located at all strategic points.  All sensors have a control range, which is continually monitored by the SPC.  If the predefined control range is exceeded or fallen below, the SPC initiates the relevant measures to adjust it.  In case of malfunction, a voice or text message is sent to up to 6 devices via a GSM module.  The inlet area of the hot exhaust gases is secured using three sensors.  If the SPC notices a deviation of the three sensors greater than the preset tolerance, then the exhaust gas inlet is interrupted and the drying operation is stopped.  Additional temperature sensors are installed in each of the drying chambers. 

The dryer is controlled in its throughput by the chamber temperatures.  A minimum temperature is predefined to start the drying.  If this is not achieved, the automatic operation of the dryer does not start.  If a chamber temperature is detected to be above the control temperature, the energy inlet is interrupted and the dryer is turned off.  The relevant information is sent to those responsible via the communication module. 

  • Motor Surveillance

A separate frequency converter monitors each motor and drive unit.  The engine load of each individual motor is determined through the current consumption, evaluated for control measure in the SPC and recorded.  If the control range of an individual drive unit is above or below specifications, the SPC initiates the relevant measures.  If there is a recognizable overload, it immediately interrupts the power supply to the motor.  At the same time, it interrupts the energy supply and turns the dryer off.  The GSM communication module sends the relevant information to those responsible. 

  • Compressed Air Monitoring

Important functions, like the opening and closing of the chamber valves and the filter cleaning, require compressed air.  If the compressed air supply is interrupted or the required minimum pressure is not present, the pressure sensor recognizes this and the SPS initiates the necessary measures.  If this occurs during operation, the energy supply is immediately interrupted and the dryer is switched off.  The relevant information is sent to those responsible. 

  • Siemens SPC Control Unit

The entire process including the material feed, the mixing, drying and subsequent pelletization is monitored by a Siemens S7 1500 SPC control unit.  All sensor data, temperatures, flow rate volumes, pressures, speeds, run times, etc. are continually recorded.  An active support unit scans the data and if deviations to the target value tolerance are noticed, then the intended requirements are carried out.  The entire process is visualized by a touchscreen panel on the HMI.

  • System-Independent Sprinkler System

Despite all the safety precautions, the high level of friction, possible foreign bodies, external faults in and outside the dryer, and faults in the electrics represent a residual risk for a fire when handling dry biomass. 

While the sensor technology in the dryer monitors all procedures, it cannot carry out any functions when the operation is switched off or without power.  The entire dryer construction is designed to be explosion proof.  The external cladding consists of F90 insulating panels with stainless steel coating.  A system independent sprinkler system is fitted to secure the plant’s products.  There is a sprinkler in each drying chamber and at all strategic points.  The water breakthrough of the sprinkler is secured by a glass cylinder, which is filled with a special fluid.

If the ambient temperature exceeds the intended threshold, then the liquid in the glass cylinder expands until it explodes.  Extinguishing water spreads into the overheated area and any possible fire is immediately extinguished.  All sprinklers are connected together in a loop.  A flow meter recognizes the triggering of the system and informs those responsible. 

  • Construction

The frame construction is produced in a modular design of strong-walled stainless steel profiles.  All elements within the drying chambers that come into contact with the material are designed in stainless steel.  All the interior cladding of the dryer rooms is non-corrosive material.  The external cladding of the dryer is produced from stainless steel profiles with 60mm of mineral wool insulation.

All material troughs are designed in corrosion-resistant stainless steel.  The entire dryer and the peripheral equipment that comes into contact with the material is designed in high-quality stainless steel for the highest degree of corrosion resistance.  All elements that come into contact with the material, which become worn out through possible wear-and-tear, are designed to be replaced.  The machine can be kept in permanent operation for an unlimited period of time.