Automated biomass distribution system

Abstract

A biomass energy system utilizes an automated biomass distribution system for evenly distributing biomass within a furnace of the biomass energy system. The even distribution of biomass dramatically increases efficiency of the biomass energy system. The automated biomass distribution system includes a control unit, a set of I/P control boxes, and a set of valve assemblies. Each valve assembly includes a pneumatic actuator, a plug and a discharge duct matching the shape of the plug.

Claims

1. An automated biomass distribution system comprising: i) a local control device unit adapted to generate a set of control signals; ii) a set of converters connected to said local control device, wherein each converter within said set of converters is adapted to receive a subset of control signals of said set of control signals and convert said received subset of control signals into a set of air pressure signals; iii) a set of actuators connected to said set of converters respectively, wherein each actuator within said set of actuators receives said set of air pressure signals from a corresponding converter within said set of converters; iv) a set of valve plugs operatively coupled to said set of actuators through a set of spindles respectively, wherein each valve plug within said set of valve plugs is actuated by a corresponding actuator within said set of actuators through a spindle within said set of spindles in response to each air pressure signal within said set of air pressure signals; and v) a set of discharge ducts operatively coupled to a set of biomass distributors, wherein: 1) said set of biomass distributors are attached to a furnace of a boiler stoker and adapted to receive biomass, wherein said furnace includes a grate for burning said biomass; 2) each discharge duct within said set of discharge ducts receives a portion of a corresponding valve plug within said set of valve plugs to form a throttling passage to regulate airflow moving into a corresponding biomass distributor through said throttling passage, wherein said airflow moves biomass over said grate, a nozzle pressure of said airflow corresponds to an air pressure signal within said set of air pressure signals, and said airflow is provided by an air supplier through a main duct; and 3) a front end of each valve plug within said set of valve plugs and a rear end of a corresponding discharge duct within said set of discharge ducts have substantially the same shape, and wherein said nozzle pressure of said airflow is increased when said throttling passage is decreased and said nozzle pressure of said airflow is decreased when said throttling passage is increased.

2. The automated biomass distribution system of claim 1 wherein the valve plug is substantially diamond shaped.

3. The automated biomass distribution system of claim 1 wherein said central control unit runs a software program to control said nozzle pressure of said air flow from each discharge duct within said set of discharge ducts.

4. The automated biomass distribution system of claim 1 wherein said local control device is further adapted to store a set of programs wherein each program within said set of programs defines a set of programmed pulses within a cycle, each programmed pulse within said set of programmed pulses defining a first control signal sent to a corresponding converter and a duration of said first control signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Although the characteristic features of this disclosure will be particularly pointed out in the claims, the invention itself, and the manner in which it may be made and used, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part hereof, wherein like reference numerals refer to like parts throughout the several views and in which:

(2) FIG. 1 is a system diagram depicting a prior art biomass boiler spreading system.

(3) FIG. 2 is a zoomed view of a prior art biomass boiler spreading system.

(4) FIG. 3 illustrates a graph depicting the relationship between static pressure behind the air sweeping nozzle versus cycle time in a prior art sweeping system.

(5) FIG. 4 illustrates a system diagram depicting a boiler furnace with a biomass spreading system in accordance with this disclosure.

(6) FIG. 5 is a cross sectional view of a high efficiency valve assembly, with its pneumatic actuator, local control box, main header and cables connecting to a main or local control panel in accordance with this disclosure.

(7) FIG. 6 is a block diagram illustrating a boiler furnace with an improved biomass spreading system in accordance with this disclosure.

(8) FIGS. 7A and 7B are schematic drawings of the high efficiency valve with the plug in fully closed and fully open positions as constructed in accordance with this disclosure.

(9) FIGS. 7C, 7D and 7E depict graphs of the operational parameters of the high efficiency valves constructed in accordance with this disclosure.

(10) FIG. 8 depicts the program selector from a local control panel constructed in accordance with this disclosure.

(11) FIGS. 9A, 9B, 9C and 9D depict graphs of nozzle pressure versus cycle time for a system constructed in accordance with this disclosure.

(12) FIGS. 10A and 10B depict graphs of nozzle pressure versus cycle time for a system constructed in accordance with this disclosure.

(13) FIG. 11A depicts a schematic drawing of a stoker boiler constructed in accordance with this disclosure.

(14) FIG. 11B is a zoomed view of FIG. 11A.

(15) A person of ordinary skills in the art will appreciate that elements of the figures above are illustrated for simplicity and clarity, and are not necessarily drawn to scale. The dimensions of some elements in the figures may have been exaggerated relative to other elements to help understanding of the present teachings. Furthermore, a particular order in which certain elements, parts, components, modules, steps, actions, events and/or processes are described or illustrated may not be actually required. A person of ordinary skills in the art will appreciate that, for the purpose of simplicity and clarity of illustration, some commonly known and well-understood elements that are useful and/or necessary in a commercially feasible embodiment may not be depicted in order to provide a clear view of various embodiments in accordance with the present teachings.

DETAILED DESCRIPTION

(16) Turning to the Figures and to FIG. 4 in particular, a boiler stoker 300 with an improved biomass spreading system 302 is shown. The boiler stoker 300 includes a furnace 332 having a grate 334 and various distributors 108 through which biomass material 352 enters into the furnace 332 and falls on the grate 334. The biomass material 352 is fed into the distributors 108 by a feeder (not shown). The biomass material 352 is distributed based on the momentum of an air jet 130, which is controlled as described herein. In one implementation, the grate 334 is a pinhole grate. Alternatively, the grate 334 is a vibrating grate, or any other type of grate known to a person of ordinary skills in the art. Under grate air 338 is provided by an air supplier 310. Air 338 further flows through many holes evenly distributed in the grate 334 and mixes with the biomass material 352. When the biomass material 352 is burned, flames 354 are created inside the furnace 332. When the biomass material 352 is evenly distributed over the grate 334 by the system 302, the flames 354 are usually short flames. Furthermore, short flames cover the entire area of the grate 334, and thus create stable combustion inside an interior chamber of the furnace 332.

(17) The improved biomass distribution system 302 includes a central control unit 304, such as a Programmable Logic Controller (“PLC”), Distributed Control System (“DCS”) or Supervisory Control And Data Acquisition (“SCADA”) system. The central control unit 304 generates current or voltage control signals. In one implementation, the control unit 304 is a PLC connected to an engineering workstation (not shown) and an application server (not shown), which sends the programmed control signals to individual control boxes 380. In another implementation, a local control panel 380 holds all the I/P transducers and a PLC, which contains various programs. A selector switch or a touch screen monitor allow the boiler operator to choose from various programs. The interface screen or front panel clearly indicates the application for each selector position, as depicted in FIG. 8. View port (or ports) 337 allows an operator to observe the distribution of biomass 352 over the grate 334.

(18) Referring to FIG. 5, a cross sectional view of the system 302 is shown. The current or voltage signals 601 are sent by the central control unit 304 and received by local control device 380, which can be a local control panel or local control box (or boxes). I/P (meaning current to pressure) or V/P (meaning voltage to pressure) transducers 604 within the local control device 380, convert the signals 601 into air pressure signals 602. The air pressure signals 602 are used to operate a pneumatic actuators 312. When the air pressure signal 602 is increased, an actuator spindle 315 of the actuator 312 extends forward. As the actuator spindle of the actuator 312 extends, the actuator 312 displaces a valve plug 316 within a valve housing 314 towards a contracting discharge duct 318. A spring 313, inside the pneumatic actuator 312, retracts the plug 316 when the air pressure signal 602 is decreased. As used herein, each local control device 380 and the transducer 604 within it is said to be connected and operatively coupled to a corresponding actuator 312 and the central control unit 304; and each valve plug 316 is said be to operatively coupled to a corresponding actuator 312 through a spindle 315.

(19) In other words, as the plug 316, displaces forward or retracts, it efficiently converts part of the static pressure of the air behind the plug 316, into dynamic pressure in the throttling passages 504, between the plug 316 and the contracting duct 318, and back into static pressure at the discharge duct 318. To evenly distribute the biomass material 352 over the grate 334 (see FIG. 4), the distribution system 302 provides airflow at variable pressure through the contracting discharge duct 318 which is operatively coupled to the distributor 108. As the biomass material 352 falls into the distributor 108, the airflow from the discharge duct 318 blows the biomass 352 into the furnace 332. The sweeping nozzle 131 and flange 153 operate as described in the background. In certain embodiments, an intermediate duct 154 is used to connect the distribution system 302 to the distributor 108, thereby allowing control of

(20) The air flow at a higher air pressure in the discharge duct 318 moves the biomass material 352 along a longer trajectory 340 (see FIG. 4) and delivers it to the far side of the grate 334 away from the distributor 108. In contrast, when the air pressure at the contracting discharge duct 318 is lower, the biomass material 352 travels a shorter trajectory 342 (see FIG. 4) and falls on the near side of the grate 334 that is closer to the distributor 108. The air pressure at the contracting discharge duct 318 is controlled by the valve plug 316 position, which in turn is programmed and controlled by the control unit 304 through the I/P or V/P transducers 604 inside the local control device 380.

(21) Air flows through a main duct 306 receiving air from an air supplier 311, to the valve housings 314, through openings 320 that match the valve housing inlet. The discharge duct 318 is connected to the biomass distributor 108. Each valve housing 314 incorporates a local control device 380. The biomass material 352 enters the furnace 332, while air flows into the distributor 108 from the duct 318.

(22) In one embodiment of the present teachings, each local control device 380 contains a controller or transducer which converts the control signals 601 from the central control unit 304, to pneumatic control signals 602 fed to the actuators 312. The air supplied to the converter or transducer 604, is known as instrumentation air, at a pressure higher than the air sweeping pressure. The instrumentation air pressure is usually between 60 to 100 PSI (meaning pounds per square inch). For example, the signal from the central control unit is 4-20 mA (meaning milliamps) and the pneumatic signal to the actuator 312 is 6-30 PSI. The air sweeping pressures are usually between 0.5 to 1 PSI. In another implementation a local control panel 380 contains the transducers for the valves.

(23) In one implementation, the actuator 312 is attached to the inlet housing 314 through a cover plate 317 which also provides access for inserting the valve plug 316 into the valve housing 314. The spring return pneumatic actuator 312 provides forces to displace the plug 316 with a plug spindle 315. In other words, the plug spindle 315 transfers force from the actuator 312 to the plug 316. Depending on the air pressure signal 602 that the actuator 312 receives from the local control device 380, the actuator 312 drives the plug 316 towards or away from the discharge duct 318. When lower sweeping air pressure is desired for the airflow, the plug 316 is pushed toward the discharge duct 318. Accordingly, the space between the plug 316 and the duct 318 becomes smaller, and less air flows around the plug 316 and into the duct 318. On the contrary, when higher air pressure is desired for the airflow, the plug 316 is pulled away from the discharge duct 318. Accordingly, the space between the plug 316 and the duct 318 becomes bigger, and more air flows around the plug 316 and into the duct 318. In other words, the position of the plug 316 determines the air pressure of the airflow (also referred to herein as nozzle pressure).

(24) The contoured plug 316 and the contoured discharge duct 318 are designed to embody matching physical shapes to allow precise control of the nozzle pressure while minimizing pressure losses when the highest flows are required. In one implementation, the contoured plug 316 is substantially in the shape of a diamond. Accordingly, the front end of the contoured plug 316 incorporates surfaces that are substantially parallel to the surfaces of the rear end of the duct 318. In other words, the top surface of the front end of the plug 316 is substantially parallel to the inner top surface of the rear end of the duct 318; and the bottom surface of the front end of the plug 316 is substantially parallel to the inner bottom surface of the rear end of the duct 318. Accordingly, it can be said that the front end of the plug 316 and the rear end of the duct 318 have substantially the same geometric shape. Other plug shapes may be designed in order to obtain certain flow characterizations with respect to plug positioning as it approaches the discharge duct.

(25) Referring to FIG. 6, a block diagram illustrating a boiler furnace with an improved biomass spreading system in accordance with this disclosure is depicted. The boiler furnace includes a typical furnace 332, with an automatic, programmable biomass spreading system 302 coupled to the biomass distributors 108, a video camera 702 installed on a furnace wall, a video monitor 404 receiving the video signals 401 from video camera 702 and a central control unit 304 sending control signals 601 to the local control panel 380. A boiler control room operator 403, observes the video image sent by the camera 702 and displayed on the monitor 404, identifies the position where uneven biomass distribution problems exist and the corresponding location over the grate surface. The boiler operator 403 uses a mouse 406, a keyboard 407 or a touch screen 405 to input the bed depth changes observed on the camera monitor 404 to the central control unit 304. The central control unit 304, the monitor 404, the keyboard 407, the mouse 406 and the touch screen 405 can be disposed within a central control room 309.

(26) In a separate embodiment, when a video image is not available to the central control unit 304, the local operator 408, observes the biomass distribution on the grate through view ports 337 on the furnace walls, changing the programs manually on the local control panel 380.

(27) The programs, stored in the central control unit 304 or in the local control panel 380, define the current or voltage signals sent to each high efficiency valve assembly as well as the duration of each signal. A current or voltage value held during a preprogrammed time period is referred to herein as a programmed pulse. Turning now to FIGS. 9A, 9B, 9C, and 9D, graphs of air pressure versus elapsed cycle time are shown. It can be observed that the pressure pulses can vary according to any desired relationship. These programmed air pulses 602 are sequentially emitted based on control signals 601, one after the other, to the valve actuator 312 until completing a predetermined total time. The predetermined total time is referred to herein as a valve program cycle. Each programmed pulse corresponds to a plug position of the plug 316 within the contracting discharge duct 318. Accordingly, the central control unit 304 provides for a precise control of the valve throttling passages 504 and controls the discharge duct pressure.

(28) Referring to FIGS. 7A and 7B, these figures represent two extreme positions of the valve plug—fully closed and fully opened respectively. Plug displacement is represented by dimension ‘X’ in both drawings.

(29) FIG. 7C depicts a graph of plug displacement versus actuator pressure. As As is apparent, actuator pressure gradually increases with plug displacement ‘X’.

(30) FIG. 7D depicts a graph of nozzle pressure versus plug displacement. As is apparent, nozzle pressure generally decreases with plug displacement ‘X’.

(31) FIG. 7E depicts a graph of nozzle pressure versus control signal current as measured in milliamps (mA).

(32) The aforementioned graphs have proven to be consistent from valve to valve, allowing precise repetitive pressure steps, which in turn provides predictable nozzle pressures at any time within the pre-programmed cycles.

(33) Turning to FIG. 8, in one embodiment of this disclosure, a control panel 380 incorporates an operator interface consisting of a program selector knob 700, which can be a mechanic selector switch or part of a touch screen display. In one version of this interface, the operator may choose from various programs corresponding to different flow ranges. FIG. 8 depicts four ranges: low flow 701, medium flow 702, medium high flow 703, and high flow 704. By operating the depicted knob 700, the operator (not shown) can select the desired flow range.

(34) After observation of the biomass distribution on the grate for a period of, for example, a few seconds, the operator identifies whether the biomass is depositing evenly across the depth or it is accumulating the back or front of the grate. The operator can then adjust the control as required for the proper flow range to achieve even deposition of biomass on the grate.

(35) Turning to FIGS. 9A, 9B, 9C and 9D, these figures depict equal time pressure steps generated by various positions of the interface program selecting knob. In particular, after changing the flow setting by, for example, turning knob 700 of FIG. 8, the operator can observe the impact on biomass distribution.

(36) FIG. 9A depicts nozzle pressure (as a percentage of maximum nozzle pressure) versus the percentage of cycle time for the low flow range setting 701 of FIG. 8. FIG. 9B depicts nozzle pressure (as a percentage of maximum nozzle pressure) versus the percentage of cycle time for the medium flow range setting 702 of FIG. 8. FIG. 9C depicts nozzle pressure (as a percentage of maximum nozzle pressure) versus the percentage of cycle time for the medium high flow range setting 703 of FIG. 8. FIG. 9D depicts nozzle pressure (as a percentage of maximum nozzle pressure) versus the percentage of cycle time for the high flow range setting 704 of FIG. 8.

(37) FIGS. 10A and 10B depict graphs that correspond to programs that target the medium flow range. These graphs depict nozzle pressure (as a percentage of maximum nozzle pressure) against percent of cycle time.

(38) FIG. 11 depicts a stoker boiler 500 constructed in accordance with this disclosure. As illustrated, a first observer 501 and a second observer 502 can view the operation of the boiler 500. Turning to FIG. 11B, the second observer 502 can be disposed near to the control device 380.

(39) The foregoing description of the disclosure has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. The description was selected to best explain the principles of the present teachings and practical application of these principles to enable others skilled in the art to best utilize the disclosure in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure not be limited by the specification, but be defined by the claims set forth below. For example, while various specific dimensions were disclosed to better enable a person of skill in the art to easily reproduce the disclosed device without undue experimentation, different dimensions could be used and still fall within the coverage of the claims set forth below. In addition, although narrow claims may be presented below, it should be recognized that the scope of this invention is much broader than presented by the claim(s). It is intended that broader claims will be submitted in one or more applications that claim the benefit of priority from this application. Insofar as the description above and the accompanying drawings disclose additional subject matter that is not within the scope of the claim or claims below, the additional inventions are not dedicated to the public and the right to file one or more applications to claim such additional inventions is reserved.