Furnaces – Including noncombustible fluid supply means – Hollow grate
Reexamination Certificate
1998-12-03
2001-08-07
Lazarus, Ira S. (Department: 3743)
Furnaces
Including noncombustible fluid supply means
Hollow grate
C110S300000, C110S328000, C126S15200R, C126S16300A
Reexamination Certificate
active
06269756
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to incinerator grate plates. More particularly, the present invention relates to liquid-cooled incinerator grate plates.
For burning solid materials, especially at trash incinerators, furnaces are used which employ so-called feed grates capable of accepting and feeding the material to be incinerated with a forward motion. These feed grates are composed of bars or plates some of which are mounted in stationary position while groups of others move back and forth, i.e. alternating toward and away from the feed port.
The grate as a whole commonly consists of multiple bars or plates arranged side by side and one behind the other. Slotted nozzles in the bars or plates allow combustion air to flow to the material to be incinerated.
During the incineration process the burning solids cause the grate bars or plates to heat up considerably. The combustion air flowing through the slots, which is usually preheated or limited in quantity for reasons of combustion properties, can provide very little cooling at best. Uncooled grate bars or plates thus reach relatively high temperatures, which tends to cause strong chemical corrosion and physical wear, an obviously undesirable factor.
Strongly heated grate plates expand during operation. Allowing for such expansion requires a certain amount of ‘play’. That in turn can create gaps between the grate plates which admit air into the incineration chamber. This air flow is uncontrolled which is again an undesirable factor. Excessive amounts of air also have a negative effect on the combustion process. Smaller particles can drop through the gaps and collect underneath the grate, yet another undesirable factor.
For these two underlying reasons it is desirable to cool grate plates during operation, i.e. to keep them at a constant temperature. To that end, German patent DE 196 13 507 C1 proposes a grate plate that extends across the entire path of the grate. The grate plate incorporates numerous parallel cooling channels which run in the longitudinal direction and lead to manifolds at the end.
This type of grate plate permits effective cooling without requiring an allowance for expansion gaps which would admit an undesirable air flow. Of course, extending across the entire width of the grate, the plate becomes relatively large.
EP 0621449 B1 describes a grate plate with a serpentine cooling channel which latter runs along the horizontal axis of the grate plate and !,thus perpendicular to the feed motion. Due to the meandering course of the cooling channel some sections of the channel extend in the longitudinal direction.
A cooling-water intake on one side and an outlet for the warmed-up cooling water on the other side of the grate plate produces a thermal gradient which can cause different degrees of expansion on the two sides of the grate. Different expansion coefficients in turn can cause the plate to warp and to produce cracks which are substantially wider than the thermal expansion itself. To minimize this effect, a relatively strong coolant flow is necessary. The coolant cannot be allowed to warm up much if a warping or distortion of the grate plate due to thermal expansion differentials is to be avoided. Otherwise, gaps could form between adjoining grate plates, allowing uncontrolled air to enter the combustion chamber and debris to fall through these gaps.
SUMMARY OF THE INVENTION
Briefly stated, the invention in a preferred form is a grate plate incorporating a cooling system which adapts itself to the thermal load on the grate plate.
The grate plate is provided with a cooling channel having a centrally located coolant port (useable as an inlet or an outlet) as contrasted to side ports predominantly used in the prior art. The center location of the port allows for the coolant to be centrally introduced into or removed from the grate plate. From this central point the cooling channel leads to the peripheral sections of the grate plate, supplying the coolant to, and removing it from, these sections.
The coolant warms up as it travels through the cooling channel, producing a thermal gradient along the cooling channel. Consequently, as the grate plate is heated from the top during operation, there will be a thermal gradient from the central port toward the peripheral sections of the plate, or vice versa. In any event, the heat distribution will be more or less symmetric. Depending on the direction of flow of the coolant, the grate plate may be cooled more strongly in the center or along the perimeter. Nevertheless, in relation to a longitudinal center line the temperature distribution will be essentially symmetric. That leads to a marked improvement of the expansion pattern and consequent thermal stress distribution of the grate plate due to focused cooling. This in turn avoids warping and the formation of open gaps between neighboring grate bars or plates or a jamming of movable grate plates. Solid debris can be largely prevented from falling through gaps between grate bars or plates. Moreover, the amount of the cooling water needed can be reduced and thermal differences may be generally higher which again produces a higher temperature of the cooling water, further reducing the amount required.
Central introduction and removal of the coolant makes it possible to cool larger areas of the grate plate so that, even if the perimeter is heated up, the overall thermal expansion is relatively minor. It permits eliminating thermal expansion differentials, keeping the thermal expansion of the grate plate uniformly balanced while minimizing the amount of coolant needed, and reducing thermal stress in the plate metal.
The grate plate disclosed is intended primarily for feeder grates. Accordingly, it is provided at one end with a coupling element allowing it to be connected with a grate-plate carrier such as a round rod or similarly suitable carrying element. At its opposite end the grate plate is provided with a sliding support, for instance a foot that supports it in movable fashion on a suitable countersupport which may be a leading grate plate adjoining in the forward feed direction.
For as long as the coolant port is centered between the two sides of the grate plate, it may be located closer to the sliding support or closer to the coupling element, as dictated by the design. In either case, the thermal gradient will be more or less the same in both lateral directions. It is therefore not necessary for the coolant connecting port to be centered between the forward and the rearward end of the plate, for as long as it is positioned along an imaginary line which is centered between the two sides and connects the forward and rearward ends of the plate. Preferably, the coolant port is positioned somewhat closer to the forward end of the grate plate, so that the distance ratio between it and the ends is one to two. Configuring the intake and outlet of the coolant in this fashion will maintain a sufficiently accurate thermal symmetry while providing slightly greater cooling in the forward section.
A second coolant port may be provided anywhere on the grate plate. In this case, the cooling channel between the central port and the second port, provided at a distance from the first, may be one single channel or it may be subdivided into several subchannels.
The cooling channel may be configured in different ways. For example, it may be constituted of one cavity with several drain ports along the perimeter for discharging the coolant. The intake of the coolant is provided to the central port. It is also possible to make the cooling channel spiral-shaped (round) or to lay it out along a square-corned spiral pattern. If necessary, it may be star-shaped, with subchannels radially extending outward from the central port and connecting, individually or in groups, to additional ports along the plate perimeter.
In all cases, the desired thermal pattern on the surface of the grate plate can be obtained by selecting a suitably adapted cross section of the cooling channel. For example, in the case of a radial s
Heinz Gerhard
Sachs Hans-Ulrich
Schroth Gerhard
Alix Yale & Ristas, LLP
ALSTOM Energy Systems GmbH
Circi Ljiljana V.
Lazarus Ira S.
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