Patent Application
20100122643
This invention relates to grate blocks, which are a key feature of modern waste to energy plants that incinerate refuse and capture the energy released as steam for generating electricity. As a result of changes in the composition of refuse or garbage, and particularly due to the increase in caloric value of such material, the combustion grate, which is made up of a plurality of individual grate blocks, is exposed to high thermal stresses, particularly certain individual portions thereof such as the front face of the individual grates. Furthermore, the operator of municipal waste mass burning applications typically has no control over the composition of the trash being fed into the system. At any given moment, one section of the grate can have a pile of wet yard waste while another section can have bags of high caloric or energy content plastic containers.
Due to the dual function of the combustion grate as a combustion support with ventilating means and also as a transfer or conveyance means for the material to be burned, the grate structure often includes such features as alternating fixed and movable grate sections and is a relatively complex multi-part structure. By having a uniform distribution of air beneath the grate, the basic design and operation ensures adequate oxygen for good combustion and cooling. The grate area and length is selected for sufficient residence time to allow for complete burnout, generally less than 2 percent unburned carbon content remains in the ash residue.
There are numerous factors in the combustion process that are monitored and/or attempted to be controlled. One such factor or boundary condition that is attempted to be controlled is the grate temperature. The specific control intervention involves establishing combustion temperature controls such that the average temperature of the grate layer does not exceed 300° C. with a combustion temperature of, for example, 1000° C. Local overheating of the grate layer due to heat accumulation leads to increased corrosion and an increased scale formation rate. This results in excess wear of parts of the grate within a relatively short time and extensive annual maintenance. In these annual maintenance periods, large segments of grate parts are replaced.
The prior art has recognized one preventative measure for preventing high corrosion or scaling rates and the resulting increased mechanical wear which leads to the premature destruction of larger segments of grate block is provided by cooling off the grate blocks. There are several techniques for cooling including passing a coolant such as water through a chamber in the grate blocks and forcing air through the grate blocks. Generally, when cooling air is used, the cooling air is additionally used as the primary combustion air. Thus, the control of the primary combustion air is also a temperature control measure. For forced cooling purposes, the under grate blast generally flows against the grate layer first and air passage openings in the layer, which allows the cooling medium to pass into the refuse bed to be burned where it then participates in the combustion process as the primary combustion air. Clogging of the air openings, however, leads to reduced flow and increased back pressure in the cooling air path and, consequently, to accumulation of heat at the particular point of the grate layer. This leads to thermal overstressing of the grate part, increased wear, higher scaling rates and, within a short time, the failure of portions of the grate.
Our invention solves the above-stated problems by providing an improved modular grate block that has at least one wear plate attached to the front face of the grate block. This wear plate is designed to be removed and replaced with a new wear plate and thus avoiding the cost and waste associated with replacing the entire grate block.
Our invention eliminates the wasteful and expensive practice of discarding individual grate blocks that are worn from the high temperatures and corrosive environments found in refuse incinerators. More specifically, our invention is directed to providing individual modular grate blocks that have at least one wear plate, which is preferably attached to the front face of the grate block. The grate system of our invention preferably has a plurality of rows of fixed grate blocks and a plurality of rows of movable grate blocks alternating back and forth with each individual block having a removable wear plate as described in more detail below. A reciprocal mechanism is connected to each of the rows of moveable grate blocks for moving the rows relative to the rows of the fixed grate blocks. Each of the modular grate blocks has a top section, a front face, and a pair of side walls. Each side wall extends from the top section and the front wall. Each of the side walls of the grate blocks engage the side wall of the adjacent grate block. Although it is preferred that the at least one wear plate is attached to the front face, it is within the scope of our invention to have a wear plate attached to the top section. Each grate block has a paw portion located at the lower surface of the side section wall and front face. In a preferred embodiment, the wear block extends below the paw and engages a top section of a grate block directly in front and underneath.
The wear plate our invention is preferably made of a material that is different than the material used to fabricate the grate block body. In particular, it is preferred that the wear plate comprise a harder material and more corrosion resistant than the block body. Although harder or hardened materials are typically heavier and have higher costs associated therewith, these negatives are minimized because only the wear plate is made of such hardened materials. Indeed, it would be cost prohibiting to fabricate the unitary prior art blocks from hardened materials. With regard to the wear plates of our invention the preferred materials of construction that resist wear and corrosion include chrome-nickel alloys, stainless steels, ceramics, titanium and like materials.
Another feature of the modular grate blocks of our invention is the removability of the wear plates, especially when worn wear plates must be replaced with new wear plates. Although this removability feature can be accomplished by any known connection method, it is preferred to use a press fit connection between the backside of the wear plate and the front surface of the face wall of the grate block. One type of press fit connection that is particularly preferred is where a male protrusion or nub on the wear plate engages a corresponding slot in the front wall of the block body. Preferably, the dimensions of the nub and slot are chosen such that nub is held in the slot by friction, thus preventing the wear plate from moving in either a vertical or horizontal manner. A most preferred configuration is where the nub slides into a cup shaped slot that is tapered to provide the friction press fit. Alternatively, the nub and slot could form a “dovetail” type joint or connection.
The wear plate can be fabricated to match exactly the dimensions of the front wall of the grate block or it can be smaller or larger than the front surface of the front wall. Preferably, the wear plate should match the side walls and the top wall, but extend beyond the paw or lower edge of the front face. In this manner the wear plate becomes the bearing surface for contacting the top surface of the grate block positioned in front and underneath. This will prevent the paw of the grate block from wearing because the bottom of the wear plate makes the contact with the top wall of the grate block disposed beneath.
Our invention also encompasses methods for retrofitting an existing incinerator grate system where prior art grate blocks, which do not have wear plates, are inspected, identified as being worn, and then removed and replaced with the grate blocks of our invention that have at least one wear plate. Alternatively, the entire grate system can be changed out with a system having the modular grate blocks of our invention. In addition, our invention is directed to a method where an incinerator grate block system is inspected to identify blocks having worn wear plates and then replacing those worn wear plates with new wear plates without having to remove the individual grate blocks. Basically, the method involves locating worn wear plates, popping off the worn wear plate and snapping on a new wear plate, while leaving the grate block body attached to the system. This method of repair is cost effective in that labor is greatly reduced as well as the cost of the wear plate compared to the cost of replacing the entire grate block. Moreover, the incinerator downtime is greatly reduced as is the frequency of the planned maintenance because the wear plate can be fabricated with a longer lasting material of construction.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Referring to the drawings in detail, there is illustrated a a grate block in accordance with the present invention designated generally as 40. In a preferred embodiment, the grate block according to the invention is a modular block with at least one removable wear plate. The overall design of the complete grate block is to direct air flow to allow for generally uniform burning of trash or refuse without thermal stress caused by intense combustion and cooling.
Referring to
Underlying the grates 32 are a plurality of hoppers 34. Each of the hoppers 34 is capable of gathering any trash or ash that falls through the grate 32. It is not typical for large amounts of trash or ash to fall through the grate 32 unless one of the grate blocks 40 fails. In addition, each of the hoppers 34 is connected to an air source, such as a primary air fan 36 as seen in
The movement of the movable rows 46 is accomplished by hydraulics or a motor driven actuator. The movable rows 46 over each hopper 34 are controlled as a unit and the units can each be controlled individually. The combustion furnace 20 can have the rate of movement of each section or unit of movable rows 46 be at a different rate. The combustion furnace 20 has the combustion chamber 38 arranged above the grate 42. The combustion chamber 38, on the left side of
The combustion furnace 20 with the grate block 40 arrangement as described above operates with combustion air which passes through openings in the grate blocks 40. The combustion chamber 38 is under reduced pressure which causes combustion air from the hopper, which is under positive pressure by the primary air fan 36, to be forced through the openings 120 in the grate blocks 40 as seen in
The basic structure of the trash combustion grate 32 of this invention with its essential elements is shown most clearly in
The grate blocks 40 for both the moveable rows 46 and the fixed rows 44 have a hook portion at the rear of the block that are each received by a respective block holding tube 92. The block holding tube 92 for the fixed rows 44 are each supported by at least a pair of support ribs 93. Each support rib 93 is carried by a support rail 94 as seen in
As indicated above with respect to
As indicated with respect to
Referring to
Top edge 201 of wear plate 200 is shown matching the angle of inclination defined by corner wall 104 of top wall 100, however, other designs where the angle is not matched are possible. Wear plate 200 also has holes 120 to allow combustion air to flow from underneath grate block 40. This flow of combustion air not only supplies the oxygen necessary for combustion, but also acts a heat transfer medium to cool the grate block and attached wear plate.
The means, materials, and steps for carrying out various disclosed functions may take a variety of alternative forms without departing from the invention. Thus, the expressions “means to . . . ” and “means for . . . ”, or any method step language as may be found in the specification above or the claims below, followed by a functional statement, are intended to define and cover whatever structural, physical, chemical or electrical element or structure, or whatever method step, which may now or in the future exist which carries out the recited function, whether or not precisely equivalent to the embodiment or embodiments disclosed in the specification above, i.e., other means or steps for carrying out the same function can be used; and it is intended that such expressions be given their broadest interpretation within the terms of the following claims. Likewise, the claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the invention.
