EP3076076B1 - Method for grate firings combustion management - Google Patents

Description

The invention relates to a method for combustion management in grate firing, in which a primary combustion gas is passed through the fuel through a primary combustion region and sucked in the rear grate area, a portion of the exhaust stream and the combustion process is supplied as internal recirculation gas again.

This method is suitable for grate firing with a grate, a device below the firing grate for supplying primary combustion air through the firing grate, wherein in the firebox above the grate at least one exhaust duct is provided, wherein the suction side of a fan is connected to the suction duct, whose pressure side is connected via a line with nozzles.

A generic method and a generic grate firing are from the EP 1 901 003 A1 and the EP 1 726 876 A1 known. There recirculation gas is used to reduce the amount of exhaust gas flow and to reduce pollutant emissions.

The EP 1 901 003 suggests feeding a secondary combustion gas between the addition of internal recycle gas and the primary combustion region. This secondary combustion gas is ambient air, ambient air, and external recirculation gas or only external recirculation gas that has passed through a steam generator and optionally an exhaust gas purification system. The secondary combustion gas thus has an air content to promote combustion as secondary combustion air and to reduce the amount of primary combustion gas.

The DE 10 2008 054 038 B3 describes a process in which fuel gas is withdrawn, conditioned and post-combusted in a medium grate area. Only after the energetic utilization of this fuel gas, the residual gas is supplied to the flue gas.

It is an object of the present invention to optimize such a method in such a way that a particularly good burnout of solid fuels and the lowest possible formation of nitrogen oxide are achieved.

This object is achieved with the features of the method according to claim 1.

With the method according to the invention an optimal burnout of the exhaust gases is achieved with low nitrogen oxide formation, while a stable operation at low excess air numbers of about λ = 1.1 to λ = 1.5 can be performed at the lowest possible exhaust gas volume.

Here, in the primary combustion region, a stoichiometric to highly substoichiometric reaction condition is set with λ = 1 to λ = 0.5, and the internal recirculation gas is supplied in a burn-out region that lies downstream of the primary combustion region.

It is desirable that the exhaust gases have a residence time of at least 2 seconds at a temperature of over 850 ° C in a first exhaust draft, preferably after the Rezirkulationsgaszuführung.

An improvement of the burnout can be achieved by supplying steam or an inert gas in the direction of flow to the primary combustion region as turbulence gas for generating a turbulence.

In this case, internal recirculation gas can be supplied in the flow direction before the supply of the fluidizing gas.

The primary combustion can be driven in such a substoichiometric manner over a wide range that air numbers λ can be driven well below 1, up to λ = 0.5. As a result, syngas calorific values of up to 4000 kJ / Nm ³ can be measured in the gasification area of the combustion chamber, so that a gasification process is present. In practice, in the primary combustion region upstream of the addition of the internal recirculation gas, a syngas calorific value of more than 2000 kJ / Nm ³ and preferably more than 3000 kJ / Nm ^{3 is} set.

According to the invention, it is provided that the fuel is gasified on a gasification grid, the slag burnout is ensured in the downstream burn-out grate and the gas burnout is achieved in a combustion chamber, by supplying the internal recirculation gas to the exhaust gas stream in order to burn out the gases and excess air numbers of .lambda. = 1, 1 to λ = 1.5 to reach. The combustion management can thus be controlled so that the primary fuel conversion takes place on the grate under stoichiometric conditions, the fuel is thus gasified and the combustion takes place only by the addition of the internal recirculation gas.

Due to the defined addition of primary air and the extraction of internal recirculation gas, it is possible to gasify the fuel in a compact hybrid process on a gasification grid, to control slag burning in the downstream burnout grid and to control the gas burn-out in a combustion chamber. This gasification grid and Ausbrandrost can be downstream grates or be designed as a rust. Gasification grate and Ausbrandrost can be assigned downstream air zones on a single, possibly longer running grate. These air zones may be formed as areas or chambers. The Nachbrennluftzone or Nachbrennkammer corresponds to that part of the process in which the internal recirculation gas is supplied to the exhaust gas stream to burn out the gases and reach excess air ratios of λ = 1.1 to λ = 1.5.

To carry out the method according to the invention, it is proposed that the nozzles are arranged in the flow direction as first gas feed nozzles after the furnace grate.

It is advantageous if the formation of the throttle cable and the arrangement of the nozzles are designed such that the exhaust gases reach a residence time of at least 2 seconds at a temperature of over 850 ° C. after the last supply of the internal recirculation gas.

Furthermore, it is proposed that turbulizing nozzles with an inert gas or steam connection are arranged between the combustion grate and the nozzles.

Constructively, the gasification grate and the burn-out grate can represent successive air zones on a single grate.

Figur 1

einen Längsschnitt durch eine Feuerungsanlage in schematischer Darstellung,

Figur 2

schematisch eine Luftführung gemäß der EP 1 901 003 A1 ,

Figur 3

schematisch eine erfindungsgemäße Luftführung ohne Sekundärluft,

Figur 4

schematisch die in Figur 3 gezeigte Luftführung mit zusätzlichen Düsen zur Einbringung von Dampf oder Inertgas,

Figur 5

schematisch eine Luftführung gemäß Figur 4 mit einer zusätzlichen Zuführung von externem Abgas,

Figur 6

schematisch eine Luftführung mit zusätzlicher Zuführung von internem Rezirkulationsgas unterhalb der Dampfeindüsung,

Figur 7

schematisch eine Verbrennungsführung mit einer internen Gasrezirkulation als Mischgas aus interner und externer Gasrezirkulation,

Figur 8

schematisch eine Verfahrensführung gemäß Figur 7 mit einem Zumischen von Umgebungsluft zur internen Gasrezirkulation,

Figur 9

eine beispielhafte Angabe von Luftzahlen in verschiedenen Bereichen der schematisch dargestellten Anlage,

Figur 10

schematisch den Ablauf aus Vergasung und Ausbrand,

Figur 11

schematisch Vergasung und Verbrennung des Feststoffs und Ausbrand der Abgase,

Figur 12

schematisch einen Verfahrensablauf mit interner Rezirkulation, Vergasung, Verbrennung und Ausbrand und

Figur 13

einen Längsschnitt durch eine Feuerungsanlage mit einer Verbrennungsluftführung gemäß der Figur 6.

The invention will be described in more detail with reference to the drawing. It shows

FIG. 1

a longitudinal section through a furnace in a schematic representation,

FIG. 2

schematically an air duct according to the EP 1 901 003 A1 .

FIG. 3

schematically an inventive air duct without secondary air,

FIG. 4

schematically the in FIG. 3 shown air duct with additional nozzles for the introduction of steam or inert gas,

FIG. 5

schematically an air duct according to FIG. 4 with an additional supply of external exhaust gas,

FIG. 6

schematically an air duct with additional supply of internal recirculation gas below the steam injection,

FIG. 7

schematically a combustion management with an internal gas recirculation as mixed gas from internal and external gas recirculation,

FIG. 8

schematically a process according to FIG. 7 with an admixing of ambient air for internal gas recirculation,

FIG. 9

an exemplary indication of air numbers in different areas of the system shown schematically,

FIG. 10

schematically the process of gasification and burnout,

FIG. 11

schematically gasification and combustion of the solid and burnout of the exhaust gases,

FIG. 12

schematically a procedure with internal recirculation, gasification, combustion and burnout and

FIG. 13

a longitudinal section through a furnace with a combustion air duct according to the FIG. 6 ,

In the FIG. 1 shown firing plant has a hopper 1 with subsequent Aufgabeschurre 2 for the task of the burning material on a feed table 3, are provided on the feed piston 4 back and forth to abandon the coming from the task chute 2 Brenngut on a combustion grate 5, on which the combustion takes place of the burning material, it is irrelevant whether it is an inclined or horizontal grate, no matter what principle is.

Below the Feuerungsrostes 5 a generally designated 6 means for supplying primary combustion air is arranged, the plurality of chambers. 7 to 11 may be supplied to which by means of a fan 12 via a line 13 primary combustion air. The arrangement of the chambers 7 to 11 of the grate is divided into several sub-wind zones, so that the primary combustion air can be adjusted differently according to the needs of the grate.

Above the Feuerungsrost 5 is a combustion chamber 14, which merges in the front part in a flue gas pass 15, to connect to the units, not shown, such as a waste heat boiler and an emission control system.

In the rear area of the combustion chamber 14 is bounded by a ceiling 16, a rear wall 17 and side walls 18. Gasification of the designated with 19 burning material takes place on the front part of the Feuerungsrostes 5, above which the flue gas is 15. In this area, most of the primary combustion air is supplied through the chambers 7, 8 and 9.

On the rear part of the combustion grate 5 is only largely burned out kiln, i. the slag, and in this area primary combustion air is supplied via the chambers 10 and 11 substantially only for cooling and residual burn-out of this slag.

The burnt-out parts of the material to be fired then fall into a slag discharge 20 at the end of the combustion grate 5. In the lower region of the flue 15, nozzles 21 and 22 are provided which supply internal recirculation gas from the rear region of the combustion chamber 14 to the rising exhaust gas so as to mix the exhaust gas flow and to cause an afterburning of the flammable fractions in the exhaust gas.

For this purpose, exhaust gas is exhausted in the rear part of the combustion chamber, which is bounded by the ceiling 16, the rear wall 17 and the side walls 18, which is referred to as internal recirculation gas. In the illustrated embodiment is a Suction opening 23 provided in the rear wall 17. This suction opening 23 is connected to a suction side of a fan 25, so that exhaust gas can be sucked. With the pressure side of the fan, a line 26 is connected, which supplies the extracted exhaust gas amount nozzles 27 in the upper region of the flue 15, the burn-out region 28. A portion of the recirculation gas is forwarded from there to the nozzles 21 and 22.

In the burn-out region 28 or above it, the flue gas train 15 is clearly constricted to increase the turbulence and the mixing effect of the exhaust gas flow, the nozzles 27 being located in this constricted region. However, it is also possible to provide installations or elements 29 which disturb the gas flow and thus generate turbulence.

In the flue 15 are provided on one or more levels nozzles 30 and 31 to supply steam and / or inert gas on one or more levels the exhaust gas. In addition, nozzles 32 and 33 are provided to supply external recirculation exhaust gas at one or more levels of the exhaust train 15 to the exhaust gas. This external recirculation exhaust gas, which has already passed through a steam generator and optionally an exhaust gas purification system (not shown), can be added to the internal recirculation exhaust gas, preferably in front of the fan 25, in addition to the nozzles 32 and 33. In addition, 35 ambient air can be added to the internal recirculation gas via line.

Starting from the well-known in FIG. 2 shown method for combustion gas supply according to the EP 1 901 003 A1 , show the FIGS. 3 to 8 different process variants in which the primary air at 51, the internal gas recirculation with 52, the exhaust gas with 53, the secondary air with 54, steam or inert gas with 55, external exhaust with 56 and ambient air with 57 are respectively designated.

The FIG. 3 shows that on the in FIG. 2 shown secondary air can be completely dispensed with. In FIG. 4 becomes below the recirculation gas 52 steam or inert gas 55 added. The FIG. 5 shows the external exhaust gas circulation 56 and the FIG. 6 shows an additional supply of internal recirculation gas 52 below the vapor injection 55. In the scheme according to FIG. 7 For example, a mixed gas of internal gas recirculation 52 and external gas recirculation 56 is supplied as internal recirculation gas 52 to the exhaust gas. The embodiments with external recirculation gas and air supply are not the subject of the invention.

The admixing of ambient air 57 to the internal gas recirculation 52 shows the FIG. 8 ,

The FIG. 9 shows that below the addition of the recirculation gas 52 in the flue 60 a constriction 61 can be provided, in the range of steam or inert gas 55 can be injected. In this case lambda values of 1.15, for example, lambda values of 0.5 in the region of constriction, 52 lambda values of 1.3 can be set above the firing grate, lambda values of 1.3 can be set above the feed of the internal recirculation gas, and gases in the rear region of the grate aspirated with a lambda value of 0.65 and added about it with the addition of air with a lambda value of 0.15. The area below the addition of the internal recirculation gas 52 is thus substoichiometric and forms the gasification area 62, while the area above it is superstoichiometric and serves as a burn-out area 63.

Process schemes for gasification show the FIGS. 10 to 12 , In each case, waste 70 is fed to a gasification region 71, in which garbage is gasified with primary air 72 at a lambda value far below 1 to form slag 73.

During the gasification, a syngas 74 with a calorific value of up to 4 MJ / m ^{3 is produced} , which is burned out after the addition of external recirculation gas 75 in a burnout region 76 to exhaust gas 77 with a lambda value of 1.1 to 1.5. It should be dispensed with the addition of air 78 as completely as possible.

If the slag 73 is not burned out completely in the gasification 71, the slag is followed by a combustion region 79, in which the slag 73 is burned with primary air 80 at lambda values above 1 to form slag 81 which burns out well. This combustion region leads to an exhaust gas 82 with a lambda value of> 1, which is supplied to the burn-out region 76 as an internal recirculation gas.

Claims (5)

1. A method for combustion management in grate firing systems, in which a primary combustion gas quantity (72) is guided through the fuel (70) into a primary combustion region (71) and in the rear grate region a portion of the exhaust gas flow is sucked away and this portion of the exhaust gas flow is supplied back to the combustion process as an internal recirculation gas (52, 82) wherein a stoichiometric to strongly substoichiometric reaction condition with λ = 1 to λ = 0.5 is set in the primary combustion region (71), and the internal recirculation gas (82) is supplied in a burnout region (76), which is located downstream of the primary combustion region (71) in the flow direction, the fuel (70) is gasified on a gasification grate, slag burnout is ensured in the downstream burnout grate and the gas burnout is achieved in the burnout region (76) in that the internal recirculation gas (52, 82) is supplied to the exhaust gas flow there, in order to burn out the gases and achieve excess air numbers of lambda = 1.1. to lambda = 1.5, characterized in that in a first exhaust flue, in addition to this portion of the exhaust gas flow sucked away in the rear grate region, no secondary air (54, 78) and therefore also no further recirculation gas is supplied.
2. The method according to one of the preceding claims, characterized in that after the supply (27) of the internal recirculation gas (52, 82), the exhaust gases have a dwell time of at least 2 seconds at a temperature of more than 850°C.
3. The method according to one of the preceding claims, characterized in that a fluidizing gas (55) for creating turbulence is supplied downstream of the primary combustion region (71) in the flow direction.
4. The method according to Claim 3, characterized in that the fluidizing gas (55) is steam or inert gas.
5. The method according to one of the preceding claims, characterized in that in the primary combustion region (71), upstream of the addition of the internal recirculation gas (52, 82) in the flow direction, a syngas heating value of more than 2000 kJ/Nm³ and preferably more than 3000 kJ/nm³ is set.

Images