BOGIE HEARTH ANNEALING FURNACE

Objetivo

The steel processing industry necessitates a thermical treatment of constructions in form of welded constructions, cast steel constructions or a combination of both.
The applied heat treatments are stress relieving, tempering, solution heat treatment and normalizing just to emntion the most important ones.
All procedures have in common the annealing of the construction to a certain temperature, holding the temperature for a certain amount of time and the subsequent cooling to room temperature. The energy hereby used is mostly natural gas or mineral oil transformed into heat which in a later stage is lost to the atmosphere.
This is where the following project comes in : Our aim was to considerably reduce the amount of energy used by the help of novel isolation material, optimized gas burners and a precise temperature regulating system.
The theoretical reflections had shown that energy could be saved up to an amount of 50% compared with conventional installations.
The theoretical reflections had shown that energy could be saved up to an amount of 50% compared with conventional installations. The actual running of the boogie furnace showed that energy could be saved up to 40.3% which is close to the data our theoretical reflections were based upon.L% Since these results are very much dependent on operating conditions, the amount of energy savings has to be looked at more closely. For a better understanding of the correlation between operating conditions and energy savings a more detailed description follows :L% The isolation is basically responsible for shielding the heat of the furnace atmosphere from the environment of the furnace. This concerns the walls of the furnace, its ceiling, its door and the trolley. The calculation for the heat consumption of a conventional design which is based on an annealing process at 950 deg. C results under these conditions the use of energy amounts to 145 m3/h gas which is equivalent to 0,129 t.ROE.L% Under thesame conditions as above the heat consumption of the furnace which was installed in this project the use of energy is reduced to 49.8 m3/h gas which is equivalent to 0,044 t.ROE. The results presented show an energy saving of 57% with regard to the heat consumption of the isolation. The heat consumption of the load to be annealed is the amount of energy necessary to anneal the load from room temperature to the annealing temperature, e.g. 950 deg. C. The amount of energy is a physical figure which always remains constant.L% The consumption of energy is, however, dependent on the efficiency of the furnace in this case the burners because it serves as an indicator to which degree the amount of used energy (here natural gas) is transformed into heat.L% Conventional burners have an average efficiency of 0,7 (or 70%). However, the recu-burners we used show an average efficiency of 0.8 (or 80%).L% Due to their improved efficiency the recu-burners we used save 10% of the energy during the process of heating up the load to be annealed.L% During the period of measurement the exact figures for the energy consumption were determined with the help of a gas-meter. In total 88 annealing processes were measured. The parameters for the annealing processes were demands of our customers (temperature, annealing time, load). The period of measurement lasted for half a year.L% The medium value of energy savings over all measurements is 40,3%. A closer look shows that if the holding period is more than 10 hours the savings are less than the average. The loss of heat by the isolation and by the trolley increase with holding periods longer than 10 hours. For further applications with holding-periods longer then 10 hours an additional layer of isolation should be installed to meet the rising waste heat. When the load is less than 25t the savings are better than the average. For practical use this means that also small loads can be heat treated economically.L%
The furnace designed by STAMA is a boogie furnace. This means that the load to be annealed is placed on a trolley which is then pushed into the interior of the furnace. A door in the front shuts the furnace completely. The heating up is supplied by burners which are installed inside the furnace. The switching on/off of the burners initiated by the computerized control system guarantees a regular flow of the temperature. The necessary information for the control system is supplied by thermo elements arranged in the interior of the furnace.
The carrier of the furnace consists of a steel construction with profiles. Rolled steel plates cover the construction at the surface of the furnace.
Moving now to the inside of the furnace :
Along both sides of the steel construction starting at the height of the edge of the trolley up to approx. half of the height of the construction recesses from the chambers for the burners. In the ceiling of these chambers the burners are vertically arranged.
The door of the furnace is fitted at the front and consists of two parts, namely two frames formed by hot rolled channels with rounded edges and covered by rolled steel plates on the front. The inside walls, the ceiling/ the inside of the door is isolated by multi-layer ceramic fibres.
The trolley forms the ground of the furnace. It consists of a frame construction with seven axels with two wheels each. The axels are the same as the ones used by the railway. The top of the trolley consists of fire-proof cement resistent to high pressure.
Opposite the interior of the furnace the lower side of the trolley is isolated by a labyrinth filled with sand. In the ceiling of the furnace there are six chimneys. They serve as a valve during the process of firing and remain open during the process of cooling. With the help of pneumatic positioning the control system regulates the opening/closure of the chimney flaps.
The control system consists of eight regulators. Six of them are connected by a Ni-Cr-Ni measuring line to a respective room temperature sensor. A sum regulator analyses the measurement results of the individual zones which are then passed to a programme regulator. This programme regulator compares the temperature measured with the data given by the programme. In case of deviation it performs the necessary adjustments. In order to achieve high control accuracy eight measurements per second are taken. The control accuracy thus obtained amounts to +/- 5 deg. C.
As far as the isolation of a furnace is concerned, mainly two demands have to be made. First of all the isolation has to be sufficiently heat resistent. Secondly it has to effectively dam the flow of warmth to the environment of the furnace.
To achieve this aim the heat resistent material of fire clay was used in the past. The common construction of furnaces consisted of vaults made out of fire bricks. The disadvantage of this material is its high heat storage ability.

Programa(s)

ENG-ENDEMO C - Programme (EEC) of demonstration projects and industrial pilot projects (EEC) in the energy field, 1985-1989

Tema(s)

3.4 - INDUSTRY

Convocatoria de propuestas

Data not available

Régimen de financiación

DEM - Demonstration contracts

Coordinador

STAMA-HAHNE

Aportación de la UE

Sin datos

Dirección

PO BOX 1105
59602 RÜTHEN
Alemania

Coste total