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Reconstruction of the K11 boiler in the Písek Heat and Power Plant


The subject of the reconstruction was the replacement of powder burners with a new type of jet burner including overall conditioning of the combustion and air part as well as modification of ZAT 2000 MP boiler control system.
The guaranteed result of the reconstruction should be stable boiler operation in a fully automatic mode of operating regulation from 35% to 100% of the output while achieving the rated parameters and meeting all the emission limits.


The reconstruction of the technology part of the boiler was mainly related to the replacement of powder burners, the creation of two sections of combustion air (secondary and tertiary combustion air) and the installation of jet blowers for after-combustion air supply (3+3 jet blowers on the boiler side-walls). 
The current ZAT 2000 MP measuring and control system was completed by three control circuits and two other circuits were modified.
The reconstruction of the technology part created good conditions for full utilization of the measuring and control system on the condition of precise and reliable measurement of the operating values.
The modified measuring and control system of the boiler is completely used for automatic control of all the control circuits of power control. 
The control range of the boiler without stabilization is currently between 35 and 100% of the steam output while CO carbon monoxide emissions are up to 100 mg/Nm3 and the NOx nitrogen oxide emissions are up to 400 mg/Nm3 (relating to 6% O2 in dry fuel gases).

The basic guarantee parameters after reconstruction are as follows:


Boiler steam output 35 t/h
Superheated steam temperature 445 °C
Superheated steam pressure 3,73 MPa (abs.)
Feedwater temperature 105 °C


Illustration of the jet powder burner



The reconstruction of powder boilers, in addition to the mechanical part adjustments, in principle brings unprecedented requirements for boiler measuring and control system.

The combustion air flow for burners as well as the after-combustion air flow for jet blowers was installed and measured separately. The flow through the jet blowers is set by hand regulating flaps (3 jet blowers on the left side of the boiler and 3 jet blowers on the right side of the boiler). The combustion air for burners is separated into two zones, secondary and tertiary air, and the flow is controlled by two regulating flaps with an electric servodrive. 
The current air channels with installed placings are used to distribute the combustion and after-combustion air from the air fan and air heater.
It was necessary to have available reliable measurements both of the quantity of fuel supplied to the boiler and hot air flowing to the powder burners and jet blowers of after-combustion air, and of the oxygen concentration in the wet flue gases in second boiler draught. 
It was required to ensure precise measurement of the flow through single stages of combustion and after-combustion air as well as to ensure the reliable control of these flows, manual or automatic. 
Modification of the ZAT 2000 MP control system carried out within the reconstruction complied with the foregoing conditions to the full extent.

Modifications carried out in the current measuring system are as follows:

  •  Boiler feed control (drum water levels)
  • Superheated steam temperature control
  • Combustion chamber vacuum control
  • Superheated steam discharge pressure control (power control)
  • Hot air pressure control behind the air heater
  • Burner hot air flow control
  • After-combustion hot air flow controlRegulace napájení kotle (vodní hladiny v bubnu)

Newly installed burner after annual operation


The concept of the reconstruction described above was selected with the philosophy to minimize interventions in the current boiler system as well as the costs of the newly delivered equipment.
This is reflected in the powder burner design with conditioning of the air parts of the boiler.
The individual operating and measuring elements supplied within the reconstruction of the K11 boiler are selected to comply with the requirements imposed thereon (precision, speed, protection against fouling and choking of probes etc.).
The conditions for low-emission combustion in the boiler output control range from 15 t/h to 40 t/h of steam, improved after reconstruction of the K11 boiler. The boiler combustion is stable, without pulsations and without the creation of larger prints on the combustion-chamber walls. The values of the NOx emissions will not exceed 450 mg/Nm3 at the rated power output and the CO level will not exceed 400 mg/ Nm3 at 6% O2 in dry flue gases. It is now possible to operate the boiler at a power output of 20 t/h without stabilization, with the possibility to achieve a power output of up to 10 t/h of steam with flame stabilization by the mazout burners.


Dr. Ing. Pavel Nekvapil – design, project, in-operation adjustment
Ing. Drahoslava Pelikánová – calculations, design
Ing. Pavel Depiak – realization