WO1996033371A1 - Grate with cooling device and cooling process - Google Patents

Abstract

A grate bar and a grate are disclosed with a cooling device for incineration furnaces, in particular of garbage incineration plants. The grates are particularly subjected to mechanical stresses, as well as thermal and chemical stresses, that cause changes in flame guidance, combustion quality and ultimately operation stoppages. Grate bar wear is substantially temperature-dependent. A closed, overpressure-driven cooling device is mounted on the disclosed grate. The cooling system has an expansion vessel (32), cooled grate bars (34), a recooler (35), a pump (36) or compressor and a connection (31) for filling and emptying the cooling system, besides a pressure regulating valve.

Description

 Grate with cooling device and method for cooling

description

The invention relates to a grate with cooling device and a method for cooling for incinerators, in particular

Waste incineration plants.

A grate for incinerators is usually formed by rows of grate bars that lie one above the other and extend transversely to the transport direction of the firing material.

Grate firing is also used as a tried and tested apparatus for domestic waste incineration. The individual grids are covered with grate bars. These have the task of transporting the garbage, mixing (so-called stoking) and taking over the burnout. The processes of drying, preheating, degassing, gasification and C-burnout take place in succession on the grate and thus the grate bars.

The grate bars of the grate are provided with openings (slots, gaps, holes, etc.) through which combustion air is blown.

The grids are particularly stressed by mechanical abrasion as well as thermal and chemical wear. Corresponding wear leads to changes in the fire control, the burn-out qualities and ultimately to business interruptions. The wear of the grids is essentially temperature-dependent.

Through appropriate measures, part of the supplied combustion air - so-called primary air - is used to cool the grate bars. The cooling effect depends primarily on the amount of air. The remaining part is added as secondary air for further combustion of the gases in the combustion chamber.

Due to changes in household waste, mainly with a view to higher calorific values (recycling of glass, organic materials / green waste, increased proportion of plastics / plastics) as well as increased fluctuations in the area of high calorific values, the grate temperatures increase, on the one hand due to more intensive combustion, but on the other hand also due to lower air volumes under the grate (decreasing cooling effect). The high calorific value causes a redistribution of the entire combustion air in such a way that a higher proportion is required in the combustion chamber for the combustion of the gases.

The invention is based on the problem of creating a grate that is wear-resistant when burning high-calorific materials, does not change its shape, and thus does not change the combustion behavior as well as the transport and mixing behavior in the furnace. In addition, good emergency running properties such. B. in the event of water failure and a relatively low heating of the water to less than 100 degrees Celsius, preferably to less than 50 degrees Celsius, if water is used as the cooling medium. In addition, steam formation is to be effectively prevented.

According to the invention, the problem is solved by claims 1 and 12. Advantageous developments of the invention are specified in the subclaims.

A closed, overpressure-operated cooling device is arranged on the grate according to the invention, which advantageously prevents the formation of steam within the cooling circuit and thus also within individual grate bars or grates. This cooling system advantageously consists of an expansion or compensation vessel (32), the cooled grate bars (34), a recooler (35) as well as a pump (36) or compressor and a connection (31) for filling or emptying the cooling system together with a pressure control valve (33).

When using water, the cooling medium is operated in a cooling system under excess pressure, preferably between 1 and 6 bar. This avoids the formation of steam and z. B. prevents a two-phase flow or formation of "steam cushion" with corresponding poor heat transfer. In a special embodiment, the inlet and outlet openings for the coolant are arranged at the base of the grate bar of the grate in the area of the grate bar support. As a result, the cooling medium in the grate bar and the cooling lines are guided more favorably.

A special design of the grate for incinerators is characterized in that the inlet and outlet openings of all grate bars are connected in parallel with a main inlet line and a main outlet line. The same cooling effect is achieved for all grate bars. For each grate bar there is essentially the same temperature distribution (assuming the same heat load), so that each grate bar also has approximately the same temperature-related expansion.

For individual applications, however, a plurality of grate bars of a grate lying side by side in the direction of the grate width can also be connected to one another in series, so that, for example, an adapted cooling effect of the grate bars is achieved in adaptation to the different heat loads in the middle and edge regions of the grate. In a special version with fourteen grate bars lying next to each other, for example, the first, sixth and eleventh grate bars are connected to the main feed line with their inlet opening. The fifth, tenth and fourteenth grate bars are connected to the main drain line with their drain opening. The remaining drain or inlet openings of adjacent grate bars are interconnected. In particular, it is provided to cool both the fixed rows of grate bars and the moving rows of grate bars.

According to a particularly preferred feature of the invention, between the main inlet and main outlet opening and inlet and outlet opening of the first or last grate bar of a grate bar row or a partial area of a grate bar row, in which the inlet and outlet openings of the individual grate bars are connected to one another in series, valves arranged for supplying or removing a further cooling medium, in particular air, and for interrupting the main inlet or outlet line. This has the advantage that if there is a leak in one or more grate bars in a row of grate bars, air cooling instead of water cooling used and thus the operation can be maintained until the next planned shutdown. In addition, thermally lightly loaded grate bar rows with cheaper cooling media, such as. B. air, are cooled.

The combination of several grate bar rows in parallel to grate zones with a common inlet and outlet line and valves for the inlet and outlet of a further cooling medium, in particular air, and shut-off to the main inlet and outlet line reveals a particularly economical variant.

Air outlet openings for combustion air are further preferably arranged in the head part of the grate bar of the grate. This further improves the cooling of the grate bar.

According to a special design, recesses for the exit of combustion air are also arranged in the long sides of the grate bar in order to improve the cooling.

According to a particularly preferred feature, the grate bar of a grate with a cooling device in the grate bar has at least one channel for guiding cooling water, essentially in the longitudinal direction of the grate bar. Since the longitudinal direction of the grate bar corresponds to the material feed device, particularly good cooling of the individual grate bars is thereby achieved. By cooling each individual grate bar, the heating of the cooling medium can be kept relatively low. This increases the operational reliability of the cooling and the service life of the grates or cooling system. Water is preferably used as the cooling medium. Other, higher-boiling cooling media can also be used for special applications.

The channel arranged in the grate bar of the grate preferably has two, essentially parallel sections with opposite flow directions, these being connected to a deflection arranged in the head region of the grate bar. The sections of the channel with the opposite flow direction can lie side by side or one above the other in the horizontal or vertical plane. The Channels are fluidically optimized with regard to the heat to be removed, so that the heating of the cooling liquid is not more than about 50 degrees Celsius, preferably about 20 degrees Celsius. In particular in the case of sections of the cooling channel lying approximately one above the other, these can have different cross-sectional shapes and areas. The deflection arranged in the head region of the grate bar can lie in the plane that passes through the central axes of the approximately parallel sections of the cooling channel.

The deflection is preferably guided into the area of the edge of the grate bar head resting on an adjacent row of grate bars. It is approximately U-shaped in the area of the grate bar head.

The design of the grate bar according to the invention is described using an exemplary embodiment.

Show it:

Figure 1 is a side view of the grate bar side as part of a grate;

Figure 2 is a flow diagram of a grate, in which valves for supplying and removing a further cooling medium are arranged.

FIG. 3 shows a diagram of the cooling system with which the grate bars or grate are cooled.

1 shows a grate bar 1 as part of a grate with grate bar support 2 in the area of the grate bar foot 3. The grate bar head 4 lies with the edge 5 on a grate bar of an adjacent row of grate bars. The grate bar is made of cast iron. It has a channel 6 which has approximately parallel sections (one behind the other in FIG. 1). These parallel sections are connected to one another by a deflection 7 in the area of the grate bar head 4. The channel 6 is provided with inlet and outlet openings 8. These inlet and outlet openings are preferably attached directly to the foot end of the channel 6 Air outlet openings are provided in the grate bar head 4 between and next to the legs of the U-shaped deflection 7 (not shown).

A flow diagram of a grate is shown in FIG.

Valves are located between the main inlet 10 and the main outlet line 11 of a cooling medium, in particular water, and the inlet 12 and outlet opening 13 of the first 14 and last 15 grate bars of each grate bar row, the inlet and outlet openings of the individual grate bars being connected to one another in series arranged for the supply 16 or discharge 17 of a further cooling medium, in particular air, and for interrupting the main inlet 18 or the main outlet line 19. The second cooling medium is supplied via the main feed line 20 or main discharge line 21. The arrow 22 indicates a preferred direction of waste flow.

The grate according to the invention has the advantage that the grate bars can be used without further modification of the incinerator. It therefore remains with the previous combustion technology. The mechanical transport and mixing behavior (forward / return stroke) also remain unchanged. This applies to both the weight and the stroke length and so on. The grate is also extremely wear-resistant, as the grate bars are made of cast iron as before. Therefore, the grate according to the invention also has excellent emergency running properties in the event of malfunctions, for example in the event of water failure. The grate bars and the grate preferably have the shape known hitherto, the width of the grate bars being approximately doubled, so that in one half, that is to say the grate bar width which has been customary hitherto, the cooling water is conducted forward to the head and in the second Half is returned. The parallel channel sections have a clear height of approximately 15 to 25 mm and a clear width of approximately 40 to 60 mm. The flow rate is between 0.5 and 2 m per second. The temperature of the grate bar is approximately 100 degrees Celsius in the middle between the head and foot area. This prevents corrosion due to condensation. A temperature of about 150 degrees Celsius is maintained in the area of the head part, so that there is no disadvantage with regard to the burnout behavior. In a further exemplary embodiment, the grids or the grate bars are integrated and operated in a closed, water-cooled cooling system which is under pressure. The temperature of the water is, for example, 90 ° C., which can, however, be increased to 120 ° C., and the system pressure is 1 to 6 bar, preferably 5 bar.

In this case, the cooling system pressure is advantageously set by means of a compressor which conveys air into the outer space of an expansion vessel or compensation vessel, which is separated from the water side by a bubble. The system pressure in the cooling water circuit is set via an expansion automat integrated in the expansion tank. A contact manometer starts the expansion machine's compressor as soon as a lower limit pressure is reached in the system. The compressor is switched off as soon as the pressure reaches an upper limit. If an adjustable upper limit pressure value is exceeded, e.g. B. 6 bar, air is blown off via a valve. The two switching points are preferably adjustable between 1.0 and 6.0 bar. The separation of air, which is located within the expandable bladder, advantageously prevents the cooling water from absorbing oxygen and thus promoting corrosion on the grate bars.

In Figure 3, the diagram of a cooling device is shown. Water is fed into the cooling device through the connection 31, the pressure control valve 33 protecting the system against pressures at the grate inlet above 2 bar. The pump 36 conveys the water through one or more grate bars or grate 34 and the cooling device. The expansion or compensation vessel 32 is provided with a level measuring device, with the aid of which fresh water is automatically fed into the system when the temperature falls below a lower limit and at the same time a message is sent to the control room. The water supply is automatically interrupted when an upper limit level is reached. Due to the frequency of reporting to the control room via the water feed, leaks in the system can be identified, so that appropriate measures can be initiated. Each grate bar or row of grate bars can be locked separately. In addition, a water mass flow measuring device 37, a temperature measuring device 38, 39 and a cooling system pressure measuring device 40 are provided. The fan 41 cools the recooler 35.

Claims

claims 1. Grate for incinerators, especially of Waste incineration plants, with adjacent rows of alternating fixed and movable rows of grate bars made of cooled Grate bars, characterized in that a closed, overpressure-operated cooling device is arranged on the grate. 2. Grate for incinerators according to claim 1, characterized in that at the foot (3) of the grate bars (1) inlet and outlet openings (8) are arranged in the region of the grate bar support (2). 3. Grate for incinerators according to one of claims 1 and 2, characterized in that inlet and outlet openings (8) of a plurality of adjacent grate bars are connected to one another in series. 4. Grate for incinerators according to one or more of claims 1 to 3, characterized in that inlet and outlet openings (8) of all grate bars are connected in parallel with a main inlet or a main drain line. 5. Grate for incinerators according to one of claims 1 to 4, characterized in that between the main inlet (10) and main outlet line (11) and inlet (12) and outlet opening (13) of the first (14) or last grate bar (15th ) a grate bar row, in which the inlet and outlet openings of the individual grate bars are connected in series, valves for Supply (16) or discharge (17) of a further cooling medium, in particular air, and to interrupt the main inlet (18) or main outlet line (19) are arranged. 6. Grate for incinerators according to one or more of claims 1 to 5, characterized in that that several rows of grate bars are connected to one another in parallel to grate zones and have a common inlet and outlet line in which valves for the inlet and outlet of a further cooling medium, preferably air, are arranged. 7. Grate for incinerators according to one or more of claims 1 to 6, characterized in that in the head part (4) of the grate bar (1) air outlet openings are arranged. 8. Grate for incinerators one or more of claims 1 to 7, characterized in that in the longitudinal sides of the grate bar (1) recesses for air outlet are arranged. 9. Grate for incinerators according to one or more of claims 2, 7 and 8, characterized in that in the grate bar (1) at least one channel (6) for guiding cooling water runs essentially in the longitudinal direction of the grate bar (1). 10. Grate for incinerators according to one or more of claims 2 and 7 to 9, characterized in that the channel 2 has substantially parallel sections with opposite flow directions, these being connected to a deflection (7) attached in the head region (4) of the grate bar are. 11. Grate for incinerators according to one or more of claims 2 and 7 to 10, characterized in that the deflection (7) is guided up to the area of the edge (5) of the grate bar head (4) resting on an adjacent row of grate bars, in particular in Area of the grate bar head (4) is approximately U-shaped. 12. A method for the direct cooling of grate bars and rusting of incinerators, in particular waste incineration plants, characterized in that that the cooling medium flowing through the grate rod or the grate is guided in a cooling system under excess pressure. 13. The method according to claim 12, characterized in that the excess pressure of the cooling device by means of a Compressor-coupled expansion vessel is adjustable.