Damper and blower unit providing reversible aeration for composting

[0002] The invention pertains to the forced air composting process in which the composting material is stacked in a pile or windrow over an air distribution system such as a plenum or perforated pipes connected to blowers. This process is widely used to convert sewage sludge into beneficial soil conditioner. Microorganisms generate heat as they respire and decompose the organic matter in the pile. Specified minimum temperatures are necessary to meet U.S. Environmental Protection Agency standards for reduction of pathogens, but excessive temperatures inhibit microbial activity resulting in incomplete decomposition of organic matter. Air is either blown upward through the pile, referred to herein as positive aeration, or drawn downward through the pile, referred to herein as negative aeration. The air supplies oxygen to the microorganisms, controls the process temperature by removing excess heat, and dries the compost. Positive and negative aeration each have advantages. Positive aeration is more efficient for and drying of the pile and for providing high temperatures near the surface of the pile. Negative aeration allows higher temperature in the core of the pile and allows capture of the exhaust for treatment. The most well-equipped composting plants provide both aeration modes, referred to as reversible aeration. Periodic reversal of aeration ensures that the temperature and moisture content are uniform throughout the depth of the pile and best ensure that all of the process objectives are met. The invention is a better method for providing reversible aeration capability.

[0003] Positive aeration is effected by drawing fresh air into the blower inlet and connecting the composting process air distribution system to the blower outlet. Negative aeration is effected by connecting the composting process air distribution system to the blower inlet. The blower outlet may be connected to an air pollution control device to treat the odorous exhaust gas before discharge.

[0004] The most widely used prior art is to connect ductwork to the inlet and outlet of the blower with four separate dampers, slide gates, or valves arranged such that the composting process air distribution system may be connected to either the outlet or the inlet of the blower. This design takes up excessive space and is costly. It cannot be easily automated, because four separate valves must be actuated for reversal of aeration mode.

[0005] U.S. Pat. No. 5,540,584 is for a plurality of valves linked mechanically, specifically for air flow reversal in regenerative thermal oxidizers. It is not applicable to the composting process.

[0006] A second alternative consists of a box assembly with four ports oriented at 90 degrees. Two opposing ports are connected to the blower inlet and outlet respectively. The other two ports are connected to the air distribution system and the air pollution control device respectively. An inserted plate or rotating damper blade in the assembly can provide positive aeration in one position and negative aeration by being rotated 90 degrees. U.S. Pat. No. 5,692,893 is for such a rotary valve. U.S. Pat. Nos. 3,897,800; 3,985,149; 3,773,066 and 4,842,016 are for valves of various configurations but similar function. None of the aforementioned patents are listed in classes pertaining to composting. With all of these devices, two additional valves are required to close or open the fresh air intake, so the number of valves to be actuated is reduced from four to three, and pressure drop is excessive.

[0007] A third alternative is to use manually connected flexible hoses between the blower, air distribution system,and air pollution control device. This alternative cannot be automated. A fourth alternative is to connect the flexible hoses from the blower inlet and outlets to a disk 180 degrees apart and the air distribution system and air pollution control device to a similar disk. The disks are in contact and on a common axis. Rotation of one disk relative to the other effects reversal of the aeration mode. U.S. Pat. No. 5,597,732 is for a small composting apparatus incorporating the rotating disks. It is practical only for small systems, with relatively small hose diameter.

[0008] U.S. Pat. No 3,967,779 is for an air mixing valve with a plurality of mechanically linked louvers mounted on parallel shafts inside a single assembly with multiple inlets. This valve does not pertain to air flow reversal.

[0009] The invention consists of a housing coupled to the inlet and outlet of a centrifugal blower. The housing has three ports: one connected to the composting process air distribution system; one discharging polluted process exhaust, and one for the intake of fresh air. Inside the assembly are four or more vanes pivotally mounted on parallel shafts. The shafts are fitted with co-planar crank arms, which are connected by linkages, such that all of the shafts rotate through the same angular displacement when one is rotated. When the vanes are in the first of two alternate positions the negative aeration mode is effected by connecting the blower outlet to the air pollution control device, connecting the blower inlet to the composting process air distribution system, and blocking the fresh air intake.

[0010] When the vanes are in the second position the positive aeration mode is effected by blocking the discharge to the air pollution device, opening the fresh air intake, and directing the air from the outlet of the blower to the composting process air distribution system.

[0011] The reversal of the aeration mode is therefore effected by a single actuator, which makes automation of aeration reversal practical. The primary benefit is to public health, because automated reversal of aeration will increase the probability of reducing pathogens throughout the pile. The invention forms a compact rigid unit with the blower, making it easy to install and requires little space and little external ducting, as compared with the prior art. The invention has less pressure drop than the prior art, reducing blower horsepower and energy consumption.

[0012] FIG. 1 is an isometric drawing of the invention viewed from the air intake port, showing the attached centrifugal blower, ductwork connecting to the composting process, and outlet port ductwork connecting to the air pollution control device. The actuator is removed to show the shafts, crank arms, and co-planar linkages.

[0013] FIG. 2 is an exploded isometric view showing the four rotating vanes and the base plate. The base plate is shown with several stationary vanes, against which the rotating vanes close to provide air-tight seals. In this embodiment of the invention a rotary actuator is shown. The actuator rotates over a range of one quarter turn to change the mode of the aeration. In an alternate embodiment of the invention, a linear actuator would be used and would be co-planar with the crank arms.

[0014] FIG. 3 is a horizontal cross section showing the vanes in the negative aeration mode position. Air from the composting process is drawn into inlet of the blower and discharged through the blower outlet to the air pollution control device.

[0015] FIG. 4 is a horizontal cross section showing the vanes in the positive aeration mode position. Fresh air is drawn into the inlet of the blower and is discharged through the blower to the composting process.

[0016] FIG. 5 shows a vertical cross sections of a typical aerated compost pile with air flowing in the negative direction, that is, down through the pile, into the air distribution system and discharged into the exhaust duct.

[0017] FIG. 6 shows the same cross section with the air movement in the positive direction, that is, fresh air is drawn into the invention and is forced upward through the pile from the air distribution system. FIG. 6 also shows typical control loops that may be used to initiate automatic operation of the damper.

[0018] FIG. 7 is a plan view of a typical composting process showing three aeration systems, each with air distribution pipes connected to one unit of the invention. This view shows how the invention allows one section of the pile to be in positive aeration while the adjacent section is in negative aeration.

[0019] The compost pile configuration shown in FIGS. 5, 6, and 7 is standard practice and is shown to illustrate one appropriate application of the invention.

[0020] FIG. 1 shows the exterior of the invention attached to a standard centrifugal blower (1). The device may be manufactured as part of the blower or attached to a standard blower. The body of the damper (2) and the duct connecting to the blower inlet (3) may be a single piece, as shown in the figure, or may be separate pieces joined by a flange or seam. The air intake (4) is an opening into which fresh air enters when the damper is set for the positive aeration mode. The center port (5) is connected to the composting process and may either discharge fresh air or draw in exhaust air. The discharge port (6) discharges exhaust air to the air pollution control device when the damper is set in the negative aeration mode. The figure shows the parallel shafts of the damper vanes (7), crank arms (8), and linkage (9), intended to rotate the shafts simultaneously in the same direction. In the preferred embodiment of the invention there is an actuator to rotate the shafts.

[0021] The actuator is not shown in FIG. 1. The actuator may be an electric motor with a gear reducer, termed a rotational actuator, a rack and pinion device driven by an electric motor, termed a linear actuator, or a pneumatic or hydraulic piston and cylinder. The specific type of actuator is not claimed as part of the invention and is a standard manufactured component. In an alternative embodiment of the invention the damper may be operated manually.

[0022] FIG. 2 is an exploded view of the invention, showing the four movable vanes with shafts (10). In large dampers there may be more than four vanes and shafts, to cover wider passages without requiring excessive torque to rotate each shaft. FIG. 2 shows a rotational actuator (11), which would be connected to one shaft and would rotate all of the shafts simultaneously through the crank arms and linkages. In the exploded view, the base plate (12) is shown. Inside the damper are stationary vanes (13) with which the rotating vanes make contact, in order to close off the air passages.

[0023] FIG. 3 is a horizontal cross section through the damper showing the positions of the vanes when the damper is set in the negative aeration mode. The fresh air intake port (4) is blocked by the vane (10A), so that the air entering into the blower must be exhaust drawn from the composting process through the center port (5). Vane (10C) directs the exhaust discharged from the blower outlet (15) to the exhaust port (6), which may be connected to an air pollution control device. Vanes (10B) and (10D) are in the open position. FIG. 4 is a horizontal cross section showing the vanes when the damper is set in the positive aeration mode. Vane (10A) is in the open position, allowing fresh air to enter the blower through the fresh air intake port (4). Vane (10C) is in the open position, allowing fresh air discharged by the blower to enter the composting process through the center port (5) Vanes (10B) and (10D) are in the closed position. All four vanes rotate in the same direction and through the same angle as the damper setting is changed from one aeration mode to the other.

[0024] FIG. 5 shows a typical vertical cross section through an aerated compost pile (16) in the negative aeration mode. The arrows (17) represent the direction of air movement, which is downward into the pile. The air is drawn into the air distribution system (18) at the base of the pile. The air distribution system may consist of perforated pipes in a bed of wood chips or a hollow floor in which there are air passages and openings communicating with the compost pile. The specific type of air distribution system is not claimed as part of the invention. The air distribution system is connected to the invention (2). The invention is also connected to the exhaust duct (19) that may be connected to the air pollution control device. The air pollution control device may be a biological filter, absorption scrubber, adsorption media, or thermal device, The specific type of air pollution control device is not claimed as part of this invention.

[0025] FIG. 6 shows a vertical cross section through a typical compost pile in the positive aeration mode. The arrows (17) show the exhaust discharged from the surface of the pile. Fresh air is forced into the base of the compost pile through the air distribution system. In the positive aeration mode, no exhaust is discharged to the air pollution control device. FIG. 6 also shows typical control loops that may be used to initiate the change of damper position automatically. Temperature sensors (20) measure the temperature difference between the core and the top of the pile. They are connected to a controller (21) that powers the actuator. Excessively high temperature at the core of the pile would initiate positive aeration. Low temperatures at the core would initiate negative aeration. Alternatively, a timer (22) can initiate a change of damper position.

[0026] FIG. 7 is a horizontal cross section or plan view of a typical air distribution system for a continuous aerated compost pile, with an outline of the pile (16). There are three separate independently operated blowers each connected to a separate array of air distribution pipes (18). In FIG. 7 each of the blowers is equipped with the invention. Blowers (2A) and (2C) are shown in the negative aeration mode,as indicated by the arrows, and the exhaust is discharged to the common duct connected to the air pollution control device (19). Blower (2B) is shown in the positive aeration mode, as indicated by the arrow. The figure illustrates how the invention allows various sections of the continuous pile to be operated in differing aeration modes.

[0027] The present invention is a self contained damper for reversing the flow of air to a process with the rotation if a single shaft, thereby allowing the automation of the process with a single actuator motor.

[0028] Although the present invention has been described for use in the composting process it may be applied to any aeration process in which reversal of air flow is necessary or preferred, such as drying processes and regenerative thermal air pollution control devices.

[0029] The invention may be manufactured as an integral part of a blower, or as a separate component to be attached to a standard blower. The invention may be manufactured as a box damper with separate ductwork components connecting it to the blower intake and to the center and exhaust ports, or it may be manufactured as a single unit including all connecting ductwork as shown in FIGS. 1 and 2.