HRP960224A2 - Method of extracting heat from brown coal - Google Patents

Description

The invention relates to a process for obtaining energy from brown coal, with the features of the preamble of claim 1.

Such a procedure is known as a pre-stage for final gasification in a fluidized bed (BWK 41 (1989) p. 231 - 234), As heat with a low temperature level is used for drying, this type of drying is favorable from the point of view of energy utilization. However, on the other hand, drying equipment is expensive, and brown coal has relatively large grains of up to 6 mm. Thus, coarse coal is difficult to burn completely, whereby the additional coarse grain promotes the formation of N0x.

It is also known that raw brown coal, which in its raw state can have a water content of up to 65%, is dried during grinding, for example, in a blower mill or a blower hammer mill. At the same time, the mill sucks in hot flue gases with a temperature of around 900°C from the connected hearth. This drying and grinding process produces a grind with a small grain size, which is favorable for combustion, and in addition, there is enough recirculated gas available for heat transfer in the combustion chamber and the radiation chamber. For this type of drying, heat of a high temperature level is used, which reduces the thermal utility of the plant. Furthermore, there are several mills in the hearth area, each of which supplies fuel to one group of burners. As at least one mill is always out of operation for reasons of reserve, not all burners of one plane can be supplied with fuel. Each plane of the burner thus receives fuel unevenly.

The task of the invention is to offer a process for obtaining energy from brown coal, in which the favorable usefulness of drying brown coal at a low temperature is exploited and in which the dried brown coal is burned in such a way that expensive devices for drying brown coal are equalized, and the combustion process is carried out completely, with little NOx.

This task is solved in one process according to the invention by the characteristic features of claim 1. Forms of the invention are the subject of subclaims. The method according to the invention and its advantages are explained below.

Raw lignite with a water content of 45 to 65% is properly crushed, eg to a maximum grain size of 6 mm. Finally, the crushed raw brown coal is dried at low temperatures between 50 and 150°C in a fluidized bed dryer, which is supplied with water vapor as a drying and fluidizing agent. In a fluidized bed dryer, raw brown coal is heated to about 110°C, whereby the water content is reduced to about 12%. A tubular dryer can be used instead of a fluidized bed dryer, where low-pressure steam from a steam turbine of a power plant is used as a means of heating.

Dried, relatively coarse brown coal is burned in the combustion chamber of the steam generator without the need for expensive mills and without further processing. The combustion chamber includes the combustion chamber, which passes into the radiation chamber. The radiation chamber is connected to the flue gas outlet in which the connected heating surfaces are arranged. There are burners on the walls of the combustion chamber.

Dried brown coal is fed directly to the burners using the carrier gas. Dried brown coal can also be stored first in a temporary storage (bunker), from which the burners are supplied with fuel.

The burners are designed in such a way that the brown coal in the coal-carrier gas mixture is distributed evenly and without layering in the burner openings. Burners that fulfill this task are described in German patent application 44 07 198. These burners are shaped like round burners, surrounded by an annular ventilation channel. On the part on the inlet side, the burners accept a diver and a torsion body, and in the opening of the burner a stabilization ring, on which there are segments directed inward. The segments brake the brown coal particles in the short term, so that the back-ignition speed of the components of the brown coal that come out with the gas is partially higher than their flow rate. Therefore, brown coal ignites in a controlled manner at the burner opening even with a small amount of oxygen, so that these burners can burn even with a lack of oxygen.

Combustion air is supplied to the burners in a sub-stoichiometric amount. Based on the special shape of the burner, the amount of air can be reduced to n 0.8, without CO problems arising. With such a small amount of air, the maximum combustion temperature is lowered and little NOX is produced. The remaining combustion air is blown into the combustion chamber via the nozzles as air lost during combustion.

As the dried brown coal is fed to the burners without subsequent shredding, the burners on the walls of the combustion chamber have no spatial constraints and can be freely selected. In the plane of the section, the burners are symmetrically placed and directed in such a way that the jet of fuel falls perpendicularly to the wall of the combustion chamber in the direction of the interior of the combustion chamber. In this way, unburnt gases (CO), as well as sticky or liquid components of ash that are formed during the combustion of brown coal, are kept away from the wall of the combustion chamber. Despite the sub-stereometric relations at the burner opening, damage due to corrosion on the walls is avoided.

The burners can also be directed in such a way that due to the jet of fuel coming out, a rotating flame is created, whereby the sticky or liquid components of the ash are caught on the walls of the combustion chamber. A melt flame is formed, where the temperatures in the firebox are above the melting point of brown coal ash. As much ash as possible is extracted in liquid form, which means that the flue gases have fewer ash particles, which could lead to wear of the heating surfaces of the steam generator.

Burners arranged in a horizontal plane are symmetrically supplied with fuel. In this way, an even distribution of temperature is achieved in the combustion chamber. In the vertical direction, the burners and nozzles for supplying air obtained by combustion are arranged in such a way that the safe combustion of brown coal is ensured. In addition, maximum temperatures must be avoided, so that even temperature distribution is achieved in the combustion chamber and radiation chamber and in the vertical direction. This control of temperature is possible because neither the operation of the mills nor the space required for supply lines to and from the mills has to be taken into account when arranging the burners.

In comparison with the known drying and grinding of brown coal, in the described drying process with placing dried brown coal in the hearth, the proportion of vapor containing water vapor, which is placed in the hearth with the brown coal, is missing. The heating plates of the steam generator have a smaller amount of heat transfer medium available. Thus, the volume of the combustion chambers and thus the entire steam generator can be reduced.

Partition walls can be placed in the radiation chamber, which increases the heating of the heating plates and the construction of the entire steam generator can be reduced even more.

Claims (4)

1. The procedure for obtaining energy from brown coal, in which the brown coal is dried in a fluidized bed or tube dryer at low temperatures, indicated by the fact that the dried brown coal is blown directly or after intermediate storage in the bunker indirectly through the burner into the combustion chamber of the steam generator without further shredding, that the dried brown coal in the burners burns substereometrically with an air volume of n 0.8, that the air lost during combustion is blown into the combustion chamber and/or the radiation chamber that is connected to the combustion chamber through the nozzles, that due to the symmetrical exposure of the burner pressure, a uniform combustion is achieved in the combustion chamber temperature distribution and that by the arrangement of burners and/or nozzles for the air lost by combustion in the combustion chamber and/or radiation chamber, even temperature distribution is achieved at the same height. 2. The procedure according to claim 1, characterized by the fact that the burners are directed in such a way that the sticky or liquid constituents produced during the combustion of brown coal remain far from the walls of the combustion chamber. 3. The method according to claim 1 or 2, characterized in that the heating of the heating plates in the radiation chamber is increased by the installation of partition walls. 4. Process according to claims 1 to 3, indicated by the fact that temperatures above the ash flow point are deliberately reached, in order to remove as much ash as possible in a liquid state, thereby avoiding wear due to flue gases.