DE10012895A1 - Combustion process for all fuels by means of grate firing involves supplying different amounts of oxygen to individual primary air zones - Google Patents

Abstract

The combustion process involves supplying different amounts of oxygen to the individual primary air zones. The oxygen requirement allowing for thermal value, water content and ash content, is set to an increasing level for each zone from zone 1 upwards and averages out at 1.5-2.8 over the entire primary air zone.

Description

The air distribution in the combustion process of a modern waste incineration plant location (MVA) has been a much discussed topic for a long time. With the advent of the So-called firing power control are new discussion points here ben. In addition to the conventional air distributions with a fixed air volume flow that for primary air, side wall air (if available), secondary air and Ter tiärluft exist as a further injection level above the secondary air (if available) Plants with theoretical substoichiometry in the area of the garbage bed above the Combustion grate. In these systems, the primary air is usually via individual pri Martial air zones (there are often 5 primary air zones). Both systems are local overheating in the combustion chamber has become known, leading to considerable damage the grate and the combustion chamber lining have leads.

The quantitative division into primary and secondary air and the division of the Pri Mar air to the individual primary air zones is empirical. The related Thereby, thermodynamic processes in the area of the furnace cannot be looked at.

The goal of optimal firing control must be an even distribution of the firebox temperatures over the entire firebox. This is the only way to ensure long service life for the combustion chamber elements

• - low pollutant emissions,
• - complete burnout,

can be achieved.  

So far, no firing control concepts have become known that are based on analyti basics and pursue the goal, one over the entire area to achieve even temperature distribution in the combustion chamber.

The object of the present invention is to provide the known combustion processes for Fuels of any kind using grate firing with regard to a uniform Improve temperature distribution over the firebox.

According to the invention the object is achieved in that the individual primary air zones to maintain a temperature in the range of the desired adiabatic combustion temperature of the entire combustion system are supplied with different amounts of oxygen, with an actual oxygen requirement of the fuel of λ _u = (0.2-0.4) + K (calorific value, water content, ash content) is set. K corresponds to a correction factor as a function of the influence of the calorific value, the ash content and the water content as well as any other factors influencing the firing material. An oxygen requirement of λ _u = 0.1-0.8 is set for the following primary air zones 2 to n - 1 and an oxygen requirement of λ _o = 1.5-2.8 is set for the primary air zone n.

The air distribution during grate firing is thus determined by the air distribution of primary air, secondary air and / or hot air and the distribution of the primary air the individual primary air zones designed that an even temperature distribution the fire chamber.

The combustion chamber temperature is expediently in the range of the adiabatic ver combustion temperature of the entire system and can thus be located on one desired, correspondingly low level.

According to a further feature of the invention, the primary air zone n is another Primary air zone connected as burnout zone.

The difference between the oxygen desired for the entire combustion amount contained in the combustion air and that added by the primary air  The amount of oxygen, according to a special feature, is the addition of Se secondary air and - if available - tertiary air.

Embodiment

Basically, the schematic representation of grate firing shown in FIG. 1 can be assumed. This essentially has 5 primary air zones, 2 secondary air injections and - if available - a spare air injection. The following is intended to show how the air distribution to the individual primary air zones can be carried out under the primacy of a defined combustion chamber temperature.

In FIG. 2, the characteristic function of the course of the reaction temperature for a wide range of known fuels, depending on the chosen λ value is shown. The λ value is the quotient of the atmospheric oxygen supplied and the oxygen requirement for complete combustion.

With a λ value = 1 (supply of the amount of atmospheric oxygen required for a complete combustion is necessary) results in the highest adiabatic combustion temperature temperature. By adding more combustion air (λ <1) you can achieve be known to cool the combustion process.

At a λ value <1 one is in the gasification range, which is described in general terms by the thermodynamic equilibrium position of the reactants C, CO, CO ₂ , H ₂ , H ₂ O etc.

The energy conversion takes place in accordance with the functional curve shown in FIG. 2 for the gasification area. This characteristic course of the function was proven by a large number of sample calculations with the most varied types of waste and other types of fuel.

If you determine a suitable firebox temperature for a particular firing system, then when entering this temperature (T _zul ) in Fig. 2 as a constant (horizontal function curve) two intersection points with the "bell curve" shown.

If one plumbs these points of intersection on the abscissa, one obtains the λ values λ _u and λ _o . At λ ≦ λ _u , the desired temperature is reached or fallen below. The same applies to λ ≧ λ _o .

The determination of the primary air quantity λ _u for the primary air zone 1 can be determined exactly with knowledge of the functional curve according to FIG. 2 for the garbage introduced into the zone 1. The function course can be calculated effectively using simple means. In this combustion zone, the heating, water evaporation, degassing and gasification of the imported waste usually takes place. Since these processes can be subject to considerable fluctuations, a correction factor K as a function of the influence of the calorific value, the ash content and the water content as well as any other factors must be taken into account.

Gaseous reaction products leave this zone at the top in the firebox, a modified waste is transferred to primary air zone 2. The function according to FIG. 2 must again be calculated for this modified waste so that λ _u can be determined for the primary air zone 2. The primary air volume for zone 2 is therefore available.

This process is then carried out in an equivalent way across the other primary air zones. In order to achieve a complete burnout over the entire grate length, it is necessary to determine the primary air with λ _o for the waste / fuel arriving there in the last (or if desired also penultimate) primary air zone after determining the function according to FIG. 2. This means that if the selected combustion chamber temperature is maintained, the combustion is overstoichiometric.

Of course, with increasing mass reduction over the grate length away the transport speed of the waste / fuel can be adjusted. This means that the primary air volume and its distribution is determined analytically.

At this point it should be mentioned that an empirical determination of the Primary air volume for a zone can "slip" in the range λ = 1. You can extremely high temperatures occur, which then leads to corresponding damage to the grate or the combustion chamber lining.

With the procedure described above, it is possible by an expedient Choice of the desired temperature in the individual primary air zones on ent speaking low level a certain "safety cushion" for calorific value and / or to create fluctuations in the amount of waste.  

There is also the possibility of measuring the temperature above the Combustion zones regulate the primary air volumes for the individual zones in the area of the analytically determined air volume and thus on To respond to disturbances.

Ultimately, it should be pointed out that with this procedure an "ideal" fire length on the grate is inevitable.

By determining the total amount of primary air, the total is obtained air volume (determined from the selected adiabatic combustion temperature of the Ge total system) the remaining amount of secondary air and - if available - tertiary air and / or plate air quantities.

Claims (3)

1.Procedure for supplying the combustion air in combustion processes for fuels of any kind by means of a grate furnace which is divided into n primary air zones, oxygen amounts in the form of primary air or fresh air or as a mixture of both being added in the individual primary air zones, characterized in that the Individual primary air zones to maintain a temperature in the range of the desired adiabatic combustion temperature of the entire combustion system are supplied with different amounts of oxygen, with an actual oxygen requirement of the fuel of λ _u = (0.2 - 0.4) + K for the primary air zone 1 in the area of the fuel feed (Calorific value, water content, ash content) is set, for the following primary air zones 2 to n - 1 there is an oxygen requirement of λ _u = 0.1-0.8 and the primary air zone n has an oxygen requirement of λ _o = 1.5-2, 8 corresponds. 2. Combustion process according to claim 1, characterized in that the Primary air zone n Another primary air zone connected as burnout zone is. 3. Combustion process according to claim 1, characterized in that the Difference between the acid desired for the entire combustion Amount of substance contained in the combustion air and by the primary air amount of oxygen added via the addition of secondary air, and - if available - by adding tertiary and / or plate air.