JPH02183715A - Pulverized coal flow rate controller - Google Patents

Abstract

PURPOSE: To eliminate the need of a bypass line and hence further eliminate the possibility of a bypass line being clogged, by employing a flow rate controller for pulverized coal which reduces a primary air flow rate to control the flow rate of coal in a feed pipe line. CONSTITUTION: A pulverized coal flow rate controller 20 controls a flow of coal by decreasing a flow rate of primary air 12 in a feed pipe 16. Many air jets or nozzles 26 inject air into the feed pipe 16 from a compressed gas source 22 to obstruct a normal flow of the primary air 12 in the feed pipe 16. Reduction of the primary air stream 12 is controlled with air injection pressure. Air injection pressure creates a recirculation zone 44. The size of the local recirculation zone 44 is proportional to the injection pressure, and the degree of reduction of the flow through the feed pipe 16 is proportional to the size of the recirculation zone 44. When an increase of a coal flow is required, a coal feeding speed to a pulverized 10 is increased. This ensures that more coal is distributed to all feed pipes 16 of the system. Thereafter, the coal flow actuates the pulverized coal flow rate controller 20 of each feed pipe 16 for balancing thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates generally to pulverized coal flow control systems, and more particularly, to a novel system for accurately controlling the mass flow rate of pneumatically transported pulverized coal. and a useful flow control system.

[Conventional technology]

In a pulverized coal combustion boiler, 1
A table or larger crusher is used. Pneumatically transported pulverized coal (PC) has a diameter of 20°32cm to approximately 60.96cm.
It is typically transported to each burner by pipes ranging from 8 to 24 inches. The number of burners served by one crusher may be any number from 2 to 13, served by the same number of pipes conveying the pulverized coal.

In the operation of multi-burner boilers, a good balance between all burners is required for high thermal efficiency.
It is highly desirable to maintain a high level of smoke and to maintain tight control of chimney emissions. Pulverized coal flow is the single most important process variable that needs to be controlled to obtain balanced operation between several burners. Balanced burner operation requires that the mass flow rates of both air and pulverized coal be the same between all pipes leading to the burner within certain operating limits. Each supply or feed pipe installed between the crusher and the burner is generally connected to the other supply due to the different overall length of each pipeline, as well as the different types and number of bends used in each pipeline. The pipe or feed pipeline has some hydraulic resistance. These changes in line resistance can cause primary air and coal flow imbalances between the pulverized coal supply pipelines. This imbalance must be corrected to ensure efficient combustion.

A common industry practice is to add fixed resistance orifices or smaller diameter pipe sections to the line that have a resistance lower than the desired value, as exemplified by reference numerals 8 and 9 in FIG. . The balance condition of the primary air flow in each line is confirmed by measuring the air flow in each line with a pitot tube when there is no pulverized coal flow. However, balancing only the primary air flow in the above conditions does not necessarily ensure a balanced pulverized coal flow in the system due to the asymmetric flow distribution at the outlet of the crusher and the peculiarity of the solid flow of pneumatic transport. 10% above average in a system that uses fixed resistance orifices and pipes to balance the primary airflow.
It has been reported that there are deviations in pulverized coal flow exceeding .

[Problem to be Solved by the Invention J Although a number of pulverized coal flow guidelines have been developed at various stages of industrial development, there are still no commercially available flow control systems for pulverized coal transfer lines. The main reason such systems do not exist is that it is very difficult to design reliable control elements that can meet a very demanding set of operating requirements. Namely: 1. For long-term reliable service, this control element must have high corrosion resistance even when exposed to flowing coal particles, the velocity of the primary air in the feed pipe is approximately 2133 at full load. .6 centimeters/second (approximately 70 feet/second), but at part load, high speeds such as approximately 3048 centimeters/second (approximately 100 feet/second) and approximately 1219 degrees 2 centimeters/second (approximately 40 feet/second) speeds can be as low as seconds). These high velocity moving pulverized coals are highly abrasive flow media and will attack any conventional metal intrusions or control elements in their flow.

2. This control element must not appreciably increase the pressure drop in the line; the maximum allowable increase in pressure drop varies from plant to plant, but the allowable increase is generally very small.

3. This control element must not interfere with the normal flow of primary air pneumatically transporting the pulverized coal particles when the control function is not required.

4. This control must be sensitive enough to cause small changes in the pulverized coal mass flow rate, such as 1-2%.

5. The control system should be easily modified to fit into existing plants with reasonable installation and operating costs.

U.S. Patent Application No. 07 filed May 24, 1988
/197.926 "Pulverized coal flow rate control system" is 19
US Patent Application No. 07/1 filed on October 6, 1987
No. 06.830 (see Japanese Patent Application Laid-open No. 1-118017)
This is a partial continuation application. This U.S. Patent Application No. 07/19
No. 7.926 discloses a pulverized coal flow control system in which an aspirator is connected to the outer wall of a bend in a feed pipe. The aspirator sucks a quantity of the mixture from the feed pipe and reinjects it into the grinder. the result,
The flow of the mixture is controlled through the feed pipe.

The above-mentioned pulverized coal flow control system requires a control bypass line for commutation, and therefore has the disadvantage of high installation costs. and allows for a device that can be operated and eliminates the possibility of clogging the bypass line.

[Means for Solving the Problems] The present invention solves the above problems by providing a pulverized coal flow rate control device that controls the flow rate of coal in a feed pipe by reducing the secondary air flow rate. It is. A number of jets or nozzles inject fluid, such as compressed air, into the pipe, disrupting the normal primary air flow. - The reduction of the secondary airflow is controlled by the fluid injection pressure. The injected fluid forms a local recirculation zone. The size of this local recirculation zone is proportional to the injection pressure, and the degree of flow reduction is proportional to the size of the recirculation zone.

Since the amount of coal carried by any one of a group of feed lines fed by a common crusher is proportional to the primary air flow rate of that line, a decrease in the primary air flow rate results in a decrease in the coal flow. . Therefore, this pulverized coal flow control device is designed to reduce the primary air in the feed pipe which is found to transport more coal than is necessary to balance the burner.

In one embodiment of the invention, the apparatus includes at least one supply connected to the container for supplying a stream of the parenteral mixture from the container to the point of use, including the mixture of fluid and suspended particles. The present invention comprises a container having a pipe, an injection means for controlling the flow of said mixture by injecting fluid into each feed pipe, and a control means for controlling the degree of injection. The apparatus of the present invention, which uses a plurality of injection nozzles spaced in a pipe and uses a computer to control the amount of fluid that each injection nozzle injects into the feed pipe, prevents each injection nozzle from becoming clogged when not in use. It may further include a bypass purge line to provide restricted fluid flow through each injection nozzle to prevent this.

The invention also provides the steps of: suspending solid particles within a container to form a mixture of solid particles and fluid; discharging this mixture from said container through at least one feed pipe to a point of use; the solid particles to be transported and the fluid flow to be controlled, comprising the steps of: injecting into the feed pipes to reduce the flow of said mixture; and controlling the flow of fluid being injected into each feed pipe. Provide a method of supply. The method may further include providing fluid flow through a bypass purge line to prevent clogging of the injection nozzle. The method preferably injects the fluid at an angle of about 45° to the pipe wall and against the flow of the mixture.

One aspect of the present invention is to provide an apparatus for supplying a controlled flow of pulverized coal to a pulverized coal combustion boiler.

Another aspect of the invention is to provide an apparatus for controlling fluid-transported solid particles.

Another aspect of the invention is to provide a method for providing a controlled flow of fluid-transferred solid particles.

Yet another aspect of the present invention is to provide a pulverized coal flow control device that is simple in design, robust in construction, and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims. The present invention, and
For a better understanding of the operational advantages obtained by using the invention, reference is now made to the accompanying drawings and description in which a preferred embodiment of the invention is shown.

EXAMPLE Referring now to the accompanying drawings in which the same reference numerals indicate the same or corresponding parts throughout, FIG. 1 shows a prior art device for balancing the flow rate of air-suspended pulverized coal fed to burners 5 and 6 of a computer;

For this purpose, a fixed resistance orifice pipe 8 is provided in the supply pipe 2 and a fixed resistance pipe 9 is provided in the supply pipe 3. The use of these fixed resistors can still leave an imbalance of 10% or more. Increasing boiler efficiency by %% or more is possible in many existing power plants (power plants).
It is predicted that this can be achieved by balancing the burners to reduce the unbalance of the burners.

Balancing the burner to the above efficiency requires control of three process variables: secondary air flow, secondary air flow, and pulverized coal flow. Of these, controlling pulverized coal flow rate is the most difficult, but economically the most valuable. This is difficult because (1) typical conventional solutions, such as variable orifice valves used for many single-phase fluids, are ineffective for highly aggressive pulverized coal flows; (2) flow control is achieved by adding minimal resistance to the 5 lines so that the existing primary air transfer system remains essentially intact when not in operation; It is in the fact that it has to be done. The present invention allows for more responsive and efficient control of pulverized coal flow, resulting in cost savings as well as tighter control of stack emissions. A well balanced delivery system can be achieved.

Referring now to FIG. 2, the present invention is illustrated in combination with a crusher 10 having an internal crushing wheel (not shown) for crushing a feed of coal. -Next air 12 is supplied to the mill 1 tO, which mill (container) 10
The solid particles of pulverized coal produced within the coal are suspended in air. These solid particles are conveyed out of the grinder 1110 through the outlet pipe 14. Although the output tube 4 has a bend, the bend is not important to the present invention. The outlet pipe 14 is connected to a supply or feed pipe 16 which ultimately reaches the burner of the furnace or boiler. A pulverized coal flow control device, designated generally by the reference numeral 20, is illustrated in place in each of the feed pipes 16. A computer controller 34 that measures the flow rate and is shown in FIG.
A flow meter (not shown) may be provided in each feed pipe 16 to provide a signal corresponding to this pulverized coal flow rate for communication with the pulverized coal flow rate.

FIG. 3 is a schematic configuration diagram of the pulverized coal flow rate control device 20.

Referring to FIG. 3, a plurality of air injection nozzles 26 are shown on each feed pipe 16. Of course, the injection nozzle 26 may also include a slit into the feed pipe 16. Preferably the fluid is compressed air! 22 provides air via duct 24 for injection into feed pipe 16 through nozzle 26 . The air injection pressure is controlled by the current/pressure (1/P) remotely operated by the computer 34.
) controlled by a pressure regulator 28 with a transducer 32. The I/P converter 32 is not required for manual adjustment with the manual regulator 36, and a pressure gauge 30 is provided in each feed pipe 16 to adjust the injection pressure of each line.

The injection nozzle 26 is approximately 7.62 mm outside of each feed pipe 16.
They are spaced apart by centimeters (3 inches) or about 10.16 centimeters (4 inches). Preferably a plurality of
At least one injection nozzle is located in each feed pipe 16. For example, the diameter is approximately 45.72 cm (1
8 inches) or about 40,64 centimeters (16 inches), the feed pipe 16 has a diameter of about 4.76 millimeters (371 millimeters).
Eight air injection nozzles, approximately 7.62 cm (3 inches) or 10.16 cm (4 inches) apart, are spaced outside the pipe. These injection nozzles 26
After drilling a hole in the existing feed pipe 16, or by attaching the air injection nozzle 26 to a spool piece approximately 1 foot long, the spool piece is inserted into the feed pipe 16. You can install it by doing this.

A small bypass purge line, designated generally by the reference numeral 38, provides airflow into the injection nozzle 26 to prevent clogging when the control valve 28 is inactive. The size, pressure, and details of bypass purge line 38 depend primarily on the size and number of injection nozzles 26. In FIG. 3, the bypass purge line 38 is shown as having a fixed resistor 40 and regulator 42, while in FIG. 4 it is shown as having only a fixed resistor 40.

Generally, the larger the system, the smaller the fixed resistor 40 required in the bypass purge line 38 to ensure air flow to prevent clogging. Although close, applying a pressure of 1 or 2 psig to the nozzles may be sufficient to hold the nozzles open when nozzles 26 are inactive.

The pulverized coal flow rate control device 20 is designed to control the flow of coal by reducing the flow rate of the primary air 12 in the feed pipe 16. A number of air jets or nozzles 26 inject air from the compressed gas source 22 into the feed pipe 16, disrupting the normal flow of primary air 12 through the feed pipe 16, as shown in FIG. - The reduction of the secondary air flow 12 is controlled by the air injection pressure. The air injection pressure creates a recirculation zone 44. As best illustrated in FIG. 4, the size of this local recirculation zone 44 is proportional to the injection pressure, and the degree of flow reduction in the feed pipe 16 is proportional to the size of the recirculation zone 44. 0 to do
When an increase in coal flow is required, the coal feed rate to the crusher 10 is increased. This will distribute more coal to all feed pipes 16 in the system. The coal flow is then balanced by activating the pulverized coal flow controllers 20 in each feed pipe 16. In addition to controlling the air injection pressure in each feed pipe 16, the combiator 34 monitors the flow rate through the feedback of individual flow meters located on those pipes.

As previously explained, a typical configuration of a coal distribution system includes a plurality of feed pipes, which can be any number from 2 to 13.
The pipe diameter of the feed pipe 16, which contains a plurality of burners 18 fed by one crusher 10 through 6, is approximately 2
The velocity of the primary air 12 in the feed pipe 16, which may range from about 8 inches to about 24 inches, is about 70 feet per second at full load. /second), but at part load, it has high speeds such as about 100 feet per second (3048 cm/second) and low speeds such as about 40 feet per second (1219.2 cm/second). obtain.

As illustrated in FIG. 4, the angle of the injection nozzle 26 in a preferred embodiment is preferably such that the injection nozzle 26 is angled against the flow of the mixture of transported coal particles and the primary air stream in the feed pipe 16. is approximately 45° measured from the pipe wall in the direction opposite to the flow of the mixture.

FIG. 5 shows a cross section of the feed pipe 16 in which a plurality of jets 026 are provided. Pressure gauge 30 indicates the injection pressure regulated by regulator 28 .

Based on the results of laboratory tests performed on the experimental model, the following observations were noted.

(1) In order to reduce the main flow between 0% and 15%, injection of an air flow of up to about 1% of the main flow is required.

(2) To reduce 1% of the mainstream flow, approximately 1. O3C
FM controlled air is required.

FIG. 6 is a graph illustrating the operating characteristics of a test system illustrating the type of control functionality desired for combinator system 34. For example, if a 7% reduction is desired for a particular feed pipe 16, the computer 34 may reduce the pressure by lop.
Generates a command to adjust to sig. Similarly, if a 5% reduction in feed pipe 16 is desired, the compressed air pressure is
For operation of the pulverized coal flow controller under similar conditions, it is adjusted to 6 psig.

Although the present invention was devised primarily to solve problems associated with the control of airborne coal particles in boiler plants, the present invention is more broadly applicable to any fluid transfer system that transfers solid particles. The fluid may be a gas or a liquid.

When using a liquid fluid system, a pump generates injection pressure to reduce the fluid flow rate. Alternatively, a gas can be used to reduce the fluid flow rate of the liquid transporting the solid particles.

The invention is particularly useful when the flowing medium is highly erosive.
It is useful for applications where the system cannot tolerate appreciable increases in pressure drop and where long term reliable service is required. Many processes in the petrochemical, food processing, and pharmaceutical industries transport solid particles and powders by air. Solids flow rates often need to be controlled on-line.

In order to illustrate the application example (application example) and principle of the present invention,
While specific embodiments of the invention have been illustrated and described in detail, certain alterations, changes and improvements will occur to those skilled in the art from the foregoing. All such variations, modifications and improvements have been omitted from this specification for the sake of brevity and ease of understanding, but are understood to be within the scope of the following claims. , some variations are nozzle 26
The purpose of this is to change the flow of primary air 12 in feed pipe 16 by reversing the direction of some of it. Another variation is to reduce the liquid fluid flow transporting the solid particles with jets of liquid or gaseous fluid.

4. Figure 1 shows a conventional technique for supplying pulverized coal to a burner using a fixed resistance orifice and pipe to balance the primary air against the floating pulverized coal being supplied to the burner in the combustion chamber. FIG. 2 is a schematic diagram illustrating an example of a device for transferring coal from a crusher to a burner in a boiler; FIG. The figures are a schematic configuration diagram showing one embodiment of a pulverized coal flow rate control device according to the present invention, FIG. 4 is a longitudinal cross-sectional view showing an enlarged portion of a feed pipe, and
The figure is a cross-sectional view of a feed pipe using the present invention, and FIG. 6 is a characteristic diagram showing test results obtained with an experimental model.

10: Grinding machine 12 primary air 14: Outlet pipe 16: Feed (supply) pipe 26: Nozzle 28: Pressure regulator 30: Pressure gauge 32: Current/pressure transducer :Pulverized coal flow control device :burner :Manual adjuster :Adjustor :Fixed resistance :duct two-fluid source :Recirculation band :Computer :Bypass purge line FIG. 4

Claims (10)

[Claims] (1) A control device for controlling the flow of solid particles transferred by a fluid, comprising: a container for containing a mixture of a fluid and suspended particles; and a container connected to the container to supply a flow of the mixture from the container. at least one feed pipe for controlling the flow of the mixture; injection means for injecting fluid into the at least one feed pipe to control the flow of the mixture; and control means for controlling the injection means. Characteristic control device. (2) The control device according to claim 1, wherein the injection means includes a plurality of injection nozzles in each feed pipe. 2. The control device of claim 2, further comprising: (3) a bypass purge line for providing fluid flow through the injection nozzles to prevent clogging of the injection nozzles. (4) The control device according to claim 2, wherein each of the injection nozzles has an angle that opposes the flow of the mixture. (5) A pulverized coal flow rate control device for controlling the flow of coal in a feed pipe, comprising: a pulverizer for containing a mixture of coal particles suspended in a fluid; and a pulverizer connected to the pulverizer for containing a mixture of coal particles suspended in a fluid; a plurality of injection nozzles for injecting fluid into at least one of the feed pipes to reduce the flow of the mixture; a plurality of injection nozzles for injecting fluid into at least one of the feed pipes to reduce the flow of the mixture; A pulverized coal flow rate control device comprising: a control means for controlling the injection nozzle and adjusting the amount of fluid supplied from the injection nozzle. The pulverized coal flow rate control device according to claim 5, further comprising a bypass purge line for providing a fluid flow through the injection nozzles to prevent clogging of the injection nozzles. (7) The pulverized coal flow rate control device according to claim 6, wherein each of the injection nozzles has an angle of about 45° against the flow of the mixture. (8) A method for providing a controlled flow of fluid-transferred solid particles, comprising: suspending solid particles in a container to form a mixture of solid particles and fluid; and directing the mixture through at least one feed pipe to the container. injecting fluid into at least one feed pipe to affect the flow of the mixture; and controlling the amount of fluid being injected into each feed pipe. 9. The method of claim 8, further comprising the step of: (9) providing fluid flow through a bypass purge line to prevent clogging of the injection nozzle. 10. The method of claim 9, wherein the fluid is injected at an angle that opposes the flow of the mixture.