Description Utsk; Introduction - Schmid UTSK-180 Operating Instructions Manual

2 Description UTSK

2 Description UTSK
2.1

Introduction

This automatic underfeed combustion system is designed for the economical and low-
emission combustion of forest woodchips. The energy released by combustion is used
thermally.
Depending on the heat requirements, the combustion system adjusts its capacity within
a range of 30 to 100 percent. Depending on the required capacity, the air and fuel quan-
tities are adjusted automatically. The fuel quantity is controlled depending on the
combustion temperature by varying the running time of the dosing screw. The stoker
screw transports the dosed fuel onto the combustion retort. A rotary valve is installed
upstream from the stoker to protect it against backfire. In addition an extinguishing
water supply is connected with a non-electrical, thermostatically actuated valve and a
thermostat with an electrical switching contact on the stoker inlet.
The fuel supplied with the stoker screw runs through the necessary phases required for
optimum combustion - drying, gasification (pyrolysis), combustion (oxidation) as well as
the charcoal burnout in the combustion tray and the combustion chamber. In order to
control this process, the system has two different air supply zones. The primary air zone
below the grate for drying, gasification and burnout as well as the secondary air zone in
the combustion chamber for combustion of the gases. The combustion process is moni-
tored by the two air flow measurements in the primary and secondary air ducts, the
combustion temperature as well as the lambda/excess air measurement. The arrange-
ment of the air-cooled cast ribs in the combustion tray guarantees regular combustion
to prevent swirling of solid particles. The secondary air injection is effected from three
sides, offset by 90° in the upper part of the combustion chamber to achieve optimum
mixture of the wood gases with the combustion air and therefore full burnout with low
CO values. This construction complies with the low NOx process with air stages. The
combustion chamber is lined with fireproof concrete on the combustion chamber side,
on the one hand to protect the steel construction, on the other for storing the tempera-
ture required for optimum combustion. The radiation ceiling comprises shaped stones
and serves to efficiently dry the fuel and protect the flame tube of the boiler. The
combustion chamber is air cooled to minimise the radiation losses, protect personnel
and prevent physical contact; the entire combustion system is insulated with 100 mm
insulation mats and clad with a powder-coated metal sheet. At the same time air cooling
serves to pre-heat the secondary combustion air.
The heat energy in the hot flue gas is transferred to the water in the downstream boiler.
The colder return line of the heating system is routed at the lower end of the boiler. The
warm supply is discharged at the top side. To boost the efficiency, turbulators made of
stainless metal sheets are inserted into the boiler tube passes. The boiler is positioned
directly on the combustion chamber and insulated with rockwool mats. If the heat
discharge fails, the boiler is cooled by a heat exchanger coil supplied with mains water.
The mains water is supplied with a non-electrically powered, thermostatically actuated
valve.
The solids formed during combustion flow with the hot flue gas through the boiler. After-
wards the particles are separated in a multi-cyclone that runs in accordance with the
centrifugal force principle. The multi-cyclone is mounted compactly on the boiler and
also insulated as a unit with the combustion grate / boiler and integrated into the sheet
metal cladding.
Underfeed grate UTSK
1.10 en D-17