Design and construction of a boiler house in Rannu township

The fully automatic boiler house with wood chip storage works with wood waste (bark, sawdust, etc.) with a 30-60% moisture content and a piece size of up to 100 mm. The nominal power of the boiler is 0.85 MW (at 50% humidity), and the volume of the automatic warehouse is 140 m3. An emergency generator is provided to protect the wood boiler from overheating and in case of possible power outages. The boiler has all the necessary control, safety, and monitoring devices. A mixing pump is installed to maintain the temperature of the water returning to the boiler. Products for pressure class PN16 are used as piping reinforcement. The Kamstrup Multical heat consumption meter is installed with the ULTRAFLOW water flow meter to measure the boiler’s capacity and the amount of water produced.

Fuel is loaded into the woodchip warehouse directly from the car. The fuel supply system from the warehouse to the boiler supply unit is carried out with a screw conveyor, and an auger carries out the fuel supply to the boiler. The fuel supply line is equipped with an automatically operating fire extinguishing system.

Technical description of the hot water boiler

The boiler is designed and tested according to the standard PED 97 123 EC art 3 §3. The working temperature is 110 °C, and the working pressure is 6 bar. The boiler is 5-speed, with an open bottom. The combustion chamber is calculated and designed according to the latest technologies. The combustion chamber is designed so that the temperature of the combustion gases is minimal. This means that all the heat has been used to the maximum. The boiler is welded together from certified metal, covered with 100 mm mineral wool, and later covered with sheet metal. The compressed air system DANBLAST automatically cleans boiler smoke pipes from fly ash.

1. Boiler hearth

It is water-cooled and has a movable grate. The stepped moving grate is equipped with water cooling pipes that keep the temperature constant. This cooling technology prevents the grate from becoming clogged with slag and significantly increases the service life of cast iron grates. The hearth walls are also water-cooled.

2. Movable grate

It is equipped with inter-moving stages to ensure a smooth combustion process. The grate is moved by a hydraulic cylinder connected to a hydraulic drive. The speed of movement is variable to ensure complete combustion.

3. Primary pressure

It comes through the holes in the grate. Secondary pressure comes on the side walls from the pipes located. Primary and secondary pressures are regulated separately to ensure optimal combustion.

4. Dry ash removal

Ash from the boiler and under the multicyclone is removed into an ash container with a volume of 10 m3.

5. Multicyclone

It contains several simple cyclones. Due to the high speed of movement and the efficiency of the cyclone, solid particles fall to the bottom of the cyclone. The device is externally insulated with 100 mm mineral wool and covered with a cover sheet.

6. Smoke extractor

Ensures the correct dilution in the combustion chamber, the right gas movement speed in the multi-cyclone and smokestack, is equipped with a vibration damper.

7. Control Automation

Monitors and changes all parameters in the 30…100% power range. In the control panel, it is possible to see the current useful power of the boiler and other parameters. The system has a touch display, a PLC controller, frequency converters for all fans, a frequency converter for the smoke extractor, and the corresponding operating program. The control system based on the Internet allows for checking and regulating the operation of the boiler unit via the Internet.

8. Fuel storage

The volume of the active warehouse is 140 m3. They are filling the warehouse directly from the car. There are hydraulic scrapers, a hydraulic drive, and an auger conveyor for fuel feeding. The fuel conveyor has an automatic fire extinguishing system that prevents fire from spreading to the fuel storage. This system works independently of the power supply.