Furnaces – Solid fuel feed structure – Movable grate
Reexamination Certificate
1999-01-15
2001-04-24
Lazarus, Ira S. (Department: 3743)
Furnaces
Solid fuel feed structure
Movable grate
C110S300000, C110S286000, C110S268000, C110S185000, C122S376000, C126S15200R, C126S16300A, C126S169000
Reexamination Certificate
active
06220190
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to boiler systems, and more particularly, relates to a water-cooled oscillating grate system for a boiler, for example, used with biomass fuels.
DESCRIPTION OF THE RELATED ART
Various vibrating grate boiler arrangements are known. For example, U.S. Pat. No. 4,389,978 issued Jun. 28, 1983, discloses a grate having a fuel supporting and conveying surface including a plurality of elongate longitudinally-oriented, generally V-shaped channels. Water cooling pipes are provided for base and top part of each channel. Air feed openings are provided between both sidewalls of each channel. The grate is vibrated by a motor located outwardly of the boiler shell.
U.S. Pat. No. 3,126,846 entitled INCINERATOR GRATE issued Mar. 31, 1964 discloses a grate including multiple, alternate stationary and movable grate members. The movable grate members are reciprocated relative to the stationary grate members from front to rear relative to the incinerator. Space below the grate is divided into multiple chambers that communicate with a forced air supply duct. The amount of air for combustion supplied to various sections of the grate is controlled by adjusting dampers.
U.S. Pat. No. 4,987,834 entitled SIFTINGS REMOVAL DEVICE discloses a furnace having an ash discharge system which collects and receives siftings falling from portions of an incinerator grate. The ash discharge system includes multiple hoppers disposed under a grate. Each hopper forms an air plenum for directing and controlling the flow of combustion air to the furnace.
U.S. Pat. No. 4,437,452 entitled ROTARY CONTINUOUS ASH DISCHARGE STOKER discloses a rotary continuous ash discharge stoker having a circular grate for supporting burning fuel. The circular grate includes a central stationary section and an outer rotating section or ring. The rotating ring is supported and guided on rails and rollers which allow for the complete rotation of the grate section. Pressurized air is supplied into the housing below the circular grate via a plurality of air plenums.
Effective air distribution is not easily accomplished in the many known vibrating grate systems. A need exists for an improved water-cooled vibrating grate system that facilitates efficient combustion by effective combustion air distribution.
In one known design only the air permeated water-cooled grate is vibrated. Flat bar type springs are used to support the grate. The drive consisting of a number of eccentric crank arms spread along the length of a shaft, is directly attached to the vibrating grate. Usually one crank arm for each section of grate is utilized. The common shaft i s powered by pulleys connected to an electric motor. The conveying speed of the ash on the water-cooled grate is essentially fixed and not easily electrically adjusted while it is in operation. This stoker grate design often causes excess vibration to the boiler and the surrounding structure.
Typically the vibrating grate is essentially pushed and pulled by the crank arm located at one end, its conveying stroke is not always equal or the same along its full length. Thus, the conveying of the ash over the surfaces of the grate is not uniform. A relatively large amount of input horsepower is required to drive this vibrating grate because the single input or brute force kind of drive used is not energy efficient. To compensate for the non-uniform ash movement, this kind of vibrating grate is usually declined downhill instead of being mounted horizontally. This added slope require s more vertical height. The grate sections are typically 6 feet wide sections, so that the needed full grate width dimension had to be made up in multiple sections. Steep walled hoppers are required underneath to collect the ash siftings that fall down through openings between the grate sections. The overall combination of this type of vibrating grate combined with the needed ash siftings collecting hoppers below required an excessive amount of headroom. Multiple water pipes are projected from each end of the grate to stationary water headers. This arrangement adds cost, causes excess vibration transmission, and prompts metal fatigue in the water pipes.
In many vibrating grate systems often excessive vibration is coupled to the boiler and the surrounding structure. This occurs, particularly when the grate is not effectively counter-balanced. A need exists to provide an improved water-cooled vibrating grate system that minimizes the vibration coupled to the boiler and the surrounding structure.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide an improved water-cooled, vibrating grate system. Other objects of the invention are to provide a water-cooled, vibrating grate system that provides effective, efficient and reliable operation, and that overcomes some disadvantages of prior art arrangements.
In brief, a water-cooled, vibrating grate system for a boiler for use with biomass and other fuels includes a grate unit having a top grate surface. The top grate surface includes air-flow apertures. A plurality of water-cooling pipes support the top grate surface. The plurality of water-cooling pipes are coupled to a water supply. An air plenum unit is positioned under and attached to the top grate surface. The air plenum unit is coupled to an air supply for providing combustion air through the top grate surface air-flow apertures. A vibration drive isolation assembly vibrates the grate unit.
In accordance with features of the invention, the vibration drive isolation assembly includes a longitudinally extending counterbalance member. A plurality of drive springs are supported by the counterbalance member. The drive springs are distributed across the width and the length of the enclosed grate unit. At least one vibratory motor or mechanism is installed on the counterbalance member. A plurality of isolation springs support the longitudinal counterbalance member.
In accordance with features of the invention, the air plenum unit includes multiple zones. Each zone has an associated air flow control damper for controllably providing combustion air flow. The air plenum unit receives grate ash siftings. Usually, a plurality of ash-siftings discharge openings are located at a defined discharge end of the air plenum unit. The ash siftings being directionally vibrated to the ash-siftings discharge openings. The air plenum unit is directly attached to the top grate surface to minimize under grate air leakage.
REFERENCES:
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A Bulletin by Detroit Stoker Company, entitled “Detroit Hydrograte, Water Cooled, Continuous Ash Discharge Spreader Stoker”, Bulletin No. 1501, pp. 1-4. (undated).
A single-page of a Detroit Hydrograte Bulletin by Detroit Stoker Company, entitled “Detroit Hydrograte-An advanced design spreader stoker with water-cooled, vibrating, continuous ash discharge grates”. (undated).
Page 5 of Kinergy Bulletin KDC-1, entitled “Kinergy Driven Vibrating Conveyors”, Oct., 1997.
Page 6 of Kinergy Bulletin KDB-1, entitled “Moving and Processing Bulk Solids by the Kinergy Drive System”, Jan., 1992.
Dumbaugh George David
Toupin Kevin M.
Ciric Ljiljana V.
Lazarus Ira S.
Mason, Kolehmainen Rathburn & Wyss
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