Three-pass medium-pressure boilers combusting gaseous and liquid fuels with an autonomous flue gas pass for heat
recuperation
In compliance with the requirements of standard ČSN EN 12 953 and directive EC 97/23

Design
The boiler body consists of a cylindrical shell and two reinforced bottoms. It is divided into a burner and flue gas parts.
The burner part consists of an asymmetrically bedded boiler flue, a water cooled inflective chamber and a nest of stay tubes of the second and third pass. The front inflective chamber is not cooled. It is closed with a door enabling cleaning of the generating surfaces. Boiler venting is provided by a flue gas collector in the rear part of the boiler. Flue gas discharge is realized via a chimney neck with an upper or rear outlet.
The flue gas pass consists of a nest of stay tubes - the number of stay tubes nests is in accordance with the number of connected sources and their parameters. The front part of the boiler includes a flue gas chamber with a flue gas inlet; the rear part of the boiler includes a flue gas chamber with an upper or a rear flue gas outlet.

Working principle
The flue gas part of the boiler can be used to increase the operation efficiency for existing energy sources, e.g. cogeneration unit, flue gas turbine, waste flue gas from biomass combustion, etc.
The boiler can be operated in both a mode with a concurrent operation of both parts, i.e. burner and flue gas, and also in a mode with an autonomous operation of one of them.

Efficiency
The heat contained in flue gasses leaving the conventional part of the boiler can be transferred to feed water in the exhaust-heat exchanger. Energy thus gained increases the boiler efficiency of up to 5% reducing thus the fuel consumption.

Economizer
It supplements the basic design of the boilers. It can be integrated into the flue gas collector or autonomously placed at the flue gas outlet.
The economizer provides a highly efficient heat transfer - the counter-flow principle. It consists of nests of finned or plain tubes in the flue gas channel with admission in the water chambers.

Flue gas bypass
The boiler can be added with a flue gas bypass fitted with a couple of flue gas flaps for continuous operation of the primary flue gas source without the boiler being necessary to operate or as an emergency safety element.

Maintenance
A manhole together with inspection holes enables the boiler inner inspection. The generating surfaces are easily accessible for cleaning guaranteeing thus a permanently high efficiency.

Versions
The PB-(X)-K boilers can be supplied in steam, hot-water or warm-water versions.