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Aspiration systems are used in the most different industries industry, where the air is polluted with garbage, dust and harmful substances. Modern woodworking, food, chemical production It is impossible to imagine without such equipment as an effective, modern and reliable aspiration system.

She is also mandatory element in metalworking, metallurgy, mining. Requirements for the environmental condition of production are constantly increasing, so more and more advanced aspiration systems are required. Without the use of this equipment, it would be impossible not only to be inside the production premises, but also on the street near many industrial enterprises.

Types of systems

Currently, enterprises carry out the calculation and installation of monoblock or modular type aspiration systems.

1. Monoblock design. The monoblock system is completely autonomous and mobile. It is installed next to equipment that needs waste collection. The components of a monoblock system are a fan, a filter, and a waste container.
2. Modular design. Modular aspiration systems - complex designs, manufactured according to individual order to specific customer requirements. They may include air ducts for aspiration systems, fans low pressure, separators. Such designs can work both within one workshop and be designed for a large plant.

Aspiration systems are also divided into direct-flow and recirculation. The difference is that the former, after capturing dirty air, purify it and release it into the atmosphere, while the latter, after cleaning, return the air back to the workshop.

Before installing aspiration complexes, they are developed, which necessarily includes drawing up a planar diagram based on the required power. If calculated correctly, the system can not only clean the workshop from dust and harmful substances , but also return it warm and fresh air

, thereby reducing heating costs.

• Main system components
• Cyclone. Uses centrifugal force to remove solid dust particles from the air. The particles are pressed against the walls, then settle in the discharge hole.
• Roof filters. They consist of a filter block and a receiving chamber. The air is purified and then returned indoors. These nozzles are placed on external bunkers and used instead of outdoor cyclones.
• Dust and chip catchers. They are used in enterprises engaged in wood processing.

Filtered sleeves. Inside these sleeves, the solid component of the air-dust mass is released, in other words, the air is separated from contaminants. The use of bag filters is very effective method

purification, thanks to which up to 99.9% of particles larger than 1 micron are captured. And due to the use of pulsed filter cleaning, it works as efficiently as possible, which saves energy. Installation of aspiration units does not require modifications technological processes . Because the treatment structures are made to order, they adapt to existing technical processes and fit into existing technological equipment , used, for example, in woodworking. Thanks to accurate calculation and binding to specific conditions is achieved high efficiency

work.

Waste is removed from special bins using containers, bags or pneumatic transport.

Many companies are involved in the development and installation of treatment systems. When choosing a company, carefully study the offers, based not only on advertising materials. Only a detailed conversation with specialists about the characteristics of the equipment can help draw a conclusion about the integrity of the supplier.

System calculation

In order for the aspiration system to work effectively, it is necessary to make its correct calculation. Since this is not an easy matter, this should be done by specialists with extensive experience. If the calculations are made incorrectly, the system will not work normally, and a lot of money will be spent on rework.

When making calculations, it is necessary to take into account a lot of factors. Let's look at just a few of them.

• We determine the air flow and pressure loss at each aspiration point. All this can be found in the reference literature. After determining all the costs, a calculation is carried out - you need to sum them up and divide them by the volume of the room.
• From the reference literature you need to take information about the air speed in the aspiration system for different materials.
• The type of dust collector is determined. This can be done by having data on the throughput performance of a particular dust collection device. To calculate productivity, you need to add up the air flow at all aspiration points and increase the resulting value by 5 percent.
• Calculate the diameters of the air ducts. This is done using a table taking into account the speed of air movement and its consumption. The diameter is determined individually for each section.

Even this small list of factors indicates the complexity of calculating the aspiration system. There are also more complex indicators, which only a person with specialized knowledge can calculate. higher education and work experience.

Aspiration is simply necessary in conditions modern production. It allows you to meet environmental requirements and preserve the health of your personnel.

Introduction

Local exhaust ventilation plays the most active role in the complex of engineering means for normalizing sanitary and hygienic working conditions in production premises. At enterprises associated with the processing of bulk materials, this role is played by aspiration systems (AS), ensuring the localization of dust in places of its formation. Until now, general ventilation has played an auxiliary role - it provided compensation for the air removed by the AS. Research by the Department of MOPE BelGTASM has shown that general ventilation is integral part a complex of dust removal systems (aspiration, systems to combat secondary dust formation - hydraulic flushing or dry vacuum dust collection, general ventilation).

Despite the long history of development, aspiration received a fundamental scientific and technical basis only in last decades. This was facilitated by the development of fan manufacturing and the improvement of air purification techniques from dust. The need for aspiration from the rapidly developing metallurgical industries also grew. construction industry. A number of scientific schools aimed at solving emerging environmental problems. In the field of aspiration, the Ural (Butikov S.E., Gervasyev A.M., Glushkov L.A., Kamyshenko M.T., Olifer V.D., etc.), Krivoy Rog (Afanasyev I.I., Boshnyakov E.N., etc.) became famous , Neykov O.D., Logachev I.N., Minko V.A., Sheleketin A.V. and American (Khemeon V., Pring R.) calculating the localization of dust emissions using aspiration. Technical solutions developed on their basis in the field of designing aspiration systems are enshrined in a number of regulatory and scientific-methodological materials.

Real teaching materials summarize the accumulated knowledge in the field of designing aspiration systems and centralized vacuum dust collection systems (CVA). The use of the latter is expanding especially in production, where hydraulic flushing is unacceptable for technological and construction reasons. The methodological materials intended for the training of environmental engineers complement the course “Industrial Ventilation” and provide for the development of practical skills among senior students of the specialty 05/17/09. These materials are aimed at ensuring that students are able to:

Determine the required performance of local suction pumps and CPU nozzles;

Choose rational and reliable systems pipelines with minimal energy losses;

Define required power aspiration unit and select the appropriate draft means

And they knew:

The physical basis for calculating the performance of local suction stations;

Fundamental difference hydraulic calculation CPU systems and AC air duct networks;

Structural design of shelters for reloading units and CPU nozzles;

Principles for ensuring the reliability of AS and CPU operation;

Principles for selecting a fan and features of its operation on specific system pipelines.

The guidelines are focused on solving two practical problems: “Calculation and selection of aspiration equipment ( practical task No. 1), “Calculation and selection of equipment for a vacuum system for collecting dust and spills (practical task No. 2).”

The testing of these tasks was carried out in the autumn semester of 1994 in practical classes of groups AG-41 and AG-42, to whose students the compilers express gratitude for the inaccuracies and technical errors they identified. Careful study of materials by students Titov V.A., Seroshtan G.N., Eremina G.V. gave us reason to make changes to the content and edition methodological instructions.

1. Calculation and selection of aspiration equipment

Purpose of the work: determination of the required performance of the aspiration installation servicing the system of aspiration shelters for loading areas of belt conveyors, selection of an air duct system, dust collector and fan.

The task includes:

A. Calculation of the productivity of local suction (aspiration volumes).

B. Calculation of the dispersed composition and concentration of dust in the aspirated air.

B. Selecting a dust collector.

D. Hydraulic calculation of the aspiration system.

D. Selection of a fan and an electric motor for it.

Initial data

(The numerical values ​​of the initial values ​​are determined by the number of option N. The values ​​​​for option N = 25 are indicated in parentheses).

1. Consumption of transported material

G m =143.5 – 4.3N, (G m =36 kg/s)

2. Particle density of bulk material

2700 + 40N, (=3700 kg/m 3).

3. Initial moisture content of the material

4.5 – 0.1 N, (%)

4. Geometric parameters of the transfer chute, (Figure 1):

h 1 =0.5+0.02N, ()

h 2 =1+0.02N,

h 3 =1–0.02N,

5. Types of shelters for the loading area of ​​the conveyor belt:

0 – shelters with single walls (for even N),

D – shelters with double walls (for odd N),

Conveyor belt width B, mm;

1200 (for N=1…5); 1000 (for N= 6…10); 800 (for N= 11…15),

650 (for N = 16…20); 500 (for N= 21…26).

Sf – area cross section gutters.

Rice. 1. Aspiration of the transfer unit: 1 – upper conveyor; 2 – upper cover; 3 – transfer chute; 4 – lower shelter; 5 – aspiration funnel; 6 – side outer walls; 7 – side internal walls; 8 – hard internal partition; 9 – conveyor belt; 10 – end outer walls; 11 – end inner wall; 12 – lower conveyor

Table 1. Geometric dimensions of the lower shelter, m

Table 2. Particle size distribution of the transported material

* z =100(1 – 0.15).

At N =25

Table 3. Length of sections of the aspiration network

Rice. 2. Axonometric diagrams of the aspiration system of transfer units: 1 – transfer unit; 2 – aspiration pipes (local suction); 3 – dust collector (cyclone); 4 – fan

2. Calculation of the productivity of local suction

The basis for calculating the required volume of air removed from the shelter is the air balance equation:

The air flow rate entering the shelter through the leaks (Q n; m 3 / s) depends on the area of ​​the leaks (F n, m 2) and the optimal vacuum value in the shelter (P y, Pa):

where is the density of the surrounding air (at t 0 =20 °C; =1.213 kg/m3).

To cover the loading area of ​​the conveyor, leaks are concentrated in the area of ​​contact of the outer walls with the moving conveyor belt (see Fig. 1):

where: P – perimeter of the shelter in plan, m; L 0 – shelter length, m; b – shelter width, m; – height of the conventional gap in the contact zone, m.

Table 4. The magnitude of the vacuum in the shelter (P y) and the width of the gap ()

Air flow entering the shelter through the chute, m 3 /s

where S is the cross-sectional area of ​​the gutter, m2; – the flow rate of the reloaded material at the exit from the chute (the final speed of falling particles) is determined sequentially by calculation:

a) speed at the beginning of the chute, m/s (at the end of the first section, see Fig. 1)

G=9.81 m/s 2 (5)

b) speed at the end of the second section, m/s

c) speed at the end of the third section, m/s

– coefficient of sliding of components (“ejection coefficient”) u – air speed in the chute, m/s.

The slip coefficient of components depends on the Butakov–Neikov number*

and Euler's criterion

where d is the average particle diameter of the material being handled, mm,

(10)

(if it turns out that, should be taken as the calculated average diameter; - the sum of the local resistance coefficients (k.m.c.) of the gutter and shelters

ζ in – k.m.s, air entry into the upper shelter, related to the dynamic air pressure at the end of the chute.

F in – area of ​​leaks in the upper cover, m 2 ;

* Butakov–Neykov and Euler numbers are the essence of the parameters M and N widely used in normative and educational materials.

– Ph.D. gutters (=1.5 for vertical gutters, = 90°; =2.5 if there is an inclined section, i.e. 90°); –k.m.s. rigid partition (for shelter type “D”; in shelter type “0” there is no rigid partition, in this case lane = 0);

Table 5. Values ​​for type “D” shelter

Ψ – particle drag coefficient

β – volumetric concentration of particles in the gutter, m 3 / m 3

– the ratio of the particle flow velocity at the beginning of the chute to the final flow velocity.

With the found numbers B u and E u, the slip coefficient of the components is determined for a uniformly accelerated particle flow according to the formula:

The solution to equation (15)* can be found by the method of successive approximations, assuming as a first approximation

(16)

If it turns out that φ 1

Let's look at the calculation procedure using an example.

1. Based on the given particle size distribution, we construct an integral graph of particle size distribution (using the previously found integral sum m i) and find the median diameter (Fig. 3) d m = 3.4 mm > 3 mm, i.e. we have the case of overloading lumpy material and, therefore, =0.03 m; P y =7 Pa (Table 4). In accordance with formula (10), the average particle diameter.

2. Using formula (3), we determine the area of ​​​​the leaks of the lower shelter (bearing in mind that L 0 = 1.5 m; b = 0.6 m, at B = 0.5 m (see Table 1)

F n =2 (1.5 + 0.6) 0.03 = 0.126 m 2

3. Using formula (2), we determine the flow of air entering through the leaks of the shelter

There are other formulas for determining the coefficient, including: for a flow of small particles, the speed of which is affected by air resistance.

Rice. 3. Integral graph of particle size distribution

4. Using formulas (5)… (7) we find the particle flow rates in the chute:

hence

n = 4.43 / 5.87 = 0.754.

5. Using formula (11), we determine the amount of k.m.s. gutters taking into account the resistance of shelters. When F in =0.2 m 2, according to formula (12) we have

With h/H = 0.12/0.4 = 0.3,

according to table 5 we find ζ n ep =6.5;

6. Using formula (14) we find the volumetric concentration of particles in the gutter

7. Using formula (13), we determine the drag coefficient
particles in the chute

8. Using formulas (8) and (9), we find the Butakov–Neikov number and the Euler number, respectively:

9. We determine the “ejection” coefficient in accordance with formula (16):

And, therefore, you can use formula (17) taking into account (18)… (20):

10. Using formula (4), we determine the air flow entering the lower shelter of the first transfer unit:

In order to reduce calculations, let us set the flow rate for the second, third and fourth reloading nodes

k 2 =0.9; k 3 =0.8; to 4 =0.7

We enter the calculation results in the first row of the table. 7, assuming that all reloading nodes are equipped with the same shelter, the air flow rate entering through the leaks of the i -th reloading node is Q n i = Q n = 0.278 m 3 /s. We enter the result in the second row of the table. 7, and the amount of expenses Q f i + Q n i – in the third. The amount of expenses represents the total productivity of the aspiration unit (air flow entering the dust collector - Q n) and is entered in the eighth column of this line.

Calculation of dispersed composition and dust concentration in aspirated air

Dust Density

The flow rate of air entering the exit through the chute is Q liquid (through leaks for the “O” type shelter – Q Нi = Q H), removed from the shelter – Q ai (see Table 7).

Geometric parameters of the shelter (see Fig. 1), m:

length – L 0 ; width – b; height – N.

Cross-sectional area, m:

a) aspiration pipe F in = bc.;

b) shelters between the outer walls (for departure type “O”)

c) shelters between the inner walls (for shelter type “D”)

F 1 =b 1 H;

where b is the distance between the outer walls, m; b 1 – distance between the internal walls, m; H – shelter height, m; с – length of the inlet section of the aspiration pipe, m.

In our case, with B = 500 mm, for a shelter with double walls (shelter type “D”) b = 0.6 m; b 1 =0.4 m; C =0.25 m; H =0.4 m;

F inx =0.25 0.6 =0.15 m2; F 1 =0.4 0.4 =0.16 m2.

Removing the aspiration funnel from the gutter: a) for shelter type “0” L y = L; b) for “D” type shelter L y = L –0.2. In our case, L y =0.6 – 0.2 =0.4 m.

Average air speed inside the shelter, m/s:

a) for type “D” shelter

b) for shelter type “0”

=(Q f +0.5Q H)/F 2 . (22)

Air entry speed into the aspiration funnel, m/s:

Q a /F in (23)

Diameter of the largest particle in the aspirated air, microns:

Using formula (21) or formula (22), we determine the air speed in the shelter and enter the result in line 4 of the table. 7.

Using formula (23), we determine the speed of air entry into the aspiration funnel and enter the result in line 5 of the table. 7.

Using formula (24), we determine and enter the result in line 6 of the table. 7.

Table 6. Mass content of dust particles depending on

The values ​​corresponding to the calculated value (or the nearest value) are written out from column 6 of table and the results (in shares) are entered in rows 11...16 of columns 4...7 of table. 7. You can also use linear interpolation of the table values, but you should keep in mind that the result will be obtained, as a rule, and therefore you need to adjust the maximum value (to ensure).

Determination of dust concentration

Material consumption – , kg/s (36),

Density of material particles – , kg/m 3 (3700).

Initial moisture content of the material –, % (2).

The percentage of particles in the reloaded material is smaller - , % (at = 149...137 microns, = 2 + 1.5 = 3.5%. Consumption of dust reloaded with the material - , g/s (103.536 = 1260).

Aspiration volumes – , m 3 /s (). The speed of entry into the aspiration funnel is , m/s ().

Maximum concentration of dust in the air removed by local suction from the i-th shelter (, g/m 3),

Actual dust concentration in the aspirated air

, (26)

Where - correction factor, determined by the formula

wherein

for shelters of type “D”, for shelters of type “O”; in our case (at kg/m3)

Or with W=W 0 =2%

1. In accordance with formula (25), we calculate and enter the results in the 7th line of the summary table. 7 (we divide the specified dust consumption by the corresponding numerical value of line 3, and enter the results in line 7; for convenience, we enter the value in a note, i.e. in column 8).

2. In accordance with formulas (27...29), at the established humidity, we construct a calculated relationship of type (30) to determine the correction factor, the values ​​of which are entered in line 8 of the summary table. 7.

Example. Using formula (27), we find the correction factor psi and m/s:

If the dust content of the air turns out to be significant (> 6 g/m3), it is necessary to provide engineering methods to reduce the dust concentration, for example: hydro-irrigation of the material being reloaded, reducing the speed of air entry into the aspiration funnel, installing settling elements in the shelter or using local suction separators. If by means of hydroirrigation it is possible to increase the humidity to 6%, then we will have:

At =3.007, =2.931 g/m3 and we use relation (31) as the calculated ratio for.

3. Using formula (26), we determine the actual concentration of dust in the first local suction and enter the result in line 9 of the table. 7 (the values ​​of line 7 are multiplied by the corresponding i-th suction - the values ​​of line 8).

Determination of the concentration and dispersed composition of dust in front of the dust collector

For selection dust collection unit aspiration system serving all local suction, it is necessary to find the average parameters of the air in front of the dust collector. To determine them, the obvious balance relations of the laws of conservation of the mass transported through the air ducts of dust are used (assuming that the deposition of dust on the walls of the air ducts is negligible):

For the concentration of dust in the air entering the dust collector, we have an obvious relationship:

Bearing in mind that the expense dust j-i fractions in the i –th local suction

It's obvious that

1. Multiplying in accordance with formula (32) the values ​​of line 9 and line 3 of the table. 7, we find the dust consumption in the i –th suction, and enter its values ​​in line 10. We enter the sum of these expenses in column 8.

Rice. 4. Distribution of dust particles by size before entering the dust collector

Table 7. Results of calculations of the volumes of aspirated air, dispersed composition and dust concentration in local suction and in front of the dust collector

2. Multiplying the values ​​of line 10 by the corresponding values ​​of lines 11...16, we obtain, in accordance with formula (34), the amount of dust consumption of the j-th fraction in the i-th local suction. The values ​​of these quantities are entered on lines 17...22. The row-by-row sum of these values, entered in column 8, represents the consumption of the j-th fraction in front of the dust collector, and the ratio of these sums to total consumption dust in accordance with formula (35) is the mass fraction of the j-th fraction of dust entering the dust collector. The values ​​are entered in column 8 of the table. 7.

3. Based on the distribution of dust particles by size calculated as a result of constructing an integral graph (Fig. 4), we find the size of dust particles, smaller than which the original dust contains 15.9% of the total mass of particles (µm), the median diameter (µm) and dispersion particle size distribution: .

The most widely used for cleaning aspiration emissions from dust are inertial dry dust collectors - cyclones of the TsN type; inertial wet dust collectors - cyclones - SIOT workers, coagulation wet dust collectors KMP and KTSMP, rotoclones; contact filters – bag and granular.

For handling unheated dry bulk materials, NIOGAZ cyclones are usually used with dust concentrations up to 3 g/m 3 and microns or bag filters at high dust concentrations and smaller dust sizes. At enterprises with closed water supply cycles, inertial wet dust collectors are used.

Purified air flow – , m 3 /s (1.7),

Dust concentration in the air in front of the dust collector – g/m3 (2.68).

The dispersed composition of dust in the air in front of the dust collector is (see Table 7).

The median diameter of dust particles is , µm (35.0).

Dispersion of particle size distribution – (0.64),

When choosing CN type cyclones as a dust collector, the following parameters are used (Table 8).

aspiration conveyor hydraulic duct

Table 8. Hydraulic resistance and efficiency of cyclones

Permissible concentration of dust in the air, emitted into the atmosphere, g/m 3

at m 3 /s (37)

at m 3 /s (38)

Where the coefficient taking into account the fibrogenic activity of dust is determined depending on the value of the maximum permissible concentration (MAC) of dust in the air working area:

Required degree of air purification from dust, %

Estimated degree of air purification from dust, %

(40)

where is the degree of air purification from dust j-th fractions, % (fractional efficiency - taken according to reference data).

Disperse composition of many industrial dust(at 1< <60 мкм) как и пофракционная степень их очистки и инерционных пылеуловителю подчиняется логарифмически нормальному закону распределения, и общая степень очистки определяется по формуле :

wherein

where is the diameter of particles captured by 50% in a cyclone with a diameter of Dc at an average air speed in its cross section,

– dynamic coefficient of air viscosity (at t=20 °C, =18.09–10–6 Pa–s).

Integral (41) is not resolved in quadratures, and its values ​​are determined by numerical methods. In table Figure 9 shows the function values ​​found by these methods and borrowed from the monograph.

It is not difficult to establish that

this is a probability integral, the tabulated values ​​of which are given in many mathematical reference books (see, for example,).

We will consider the calculation procedure using a specific make-up artist.

1. Permissible concentration of dust in the air after its purification in accordance with formula (37) with a maximum permissible concentration in the working area of ​​10 mg/m 3 ()

2. The required degree of air purification from dust according to formula (39) is

Such cleaning efficiency for our conditions (µm and kg/m 3) can be ensured by a group of 4 cyclones TsN-11

3. Let us determine the required cross-sectional area of ​​one cyclone:

4. Determine the estimated diameter of the cyclone:

We select the closest of the normalized series of cyclone diameters (300, 400, 500, 600, 800, 900, 1000 mm), namely m.

5. Determine the air speed in the cyclone:

6. Using formula (43), we determine the diameter of particles captured in this cyclone by 50%:

7. Using formula (42), we determine the parameter X:

The obtained result, based on the NIOGAZ method, assumes a logarithmically normal distribution of dust particles by size. In fact, the dispersed composition of dust, in the region of large particles (> 60 microns), in the aspirated air for sheltering conveyor loading areas differs from the normal-logarithmic law. Therefore, it is recommended to compare the calculated degree of purification with calculations using formula (40) or with the methodology of the MOPE department (for cyclones), based on a discrete approach to what is fairly fully covered in the course “Mechanics of Aerosols”.

An alternative way to determine the reliable value of the overall degree of air purification in dust collectors is to carry out special experimental studies and compare them with calculated ones, which we recommend for an in-depth study of the process of air purification from solid particles.

9. The concentration of dust in the air after cleaning is

those. less than acceptable.

Introduction

Local exhaust ventilation plays the most active role in the complex of engineering means for normalizing sanitary and hygienic working conditions in production premises. At enterprises associated with the processing of bulk materials, this role is played by aspiration systems (AS), ensuring the localization of dust in places of its formation. Until now, general ventilation has played an auxiliary role - it provided compensation for the air removed by the AS. Research by the Department of MOPE BelGTASM has shown that general ventilation is an integral part of a complex of dust removal systems (aspiration, systems for combating secondary dust formation - hydraulic flushing or dry vacuum dust collection, general ventilation).

Despite the long history of development, aspiration has received a fundamental scientific and technical basis only in recent decades. This was facilitated by the development of fan manufacturing and the improvement of air purification techniques from dust. The need for aspiration from the rapidly developing sectors of the metallurgical construction industry also grew. A number of scientific schools have emerged aimed at solving emerging environmental problems. In the field of aspiration, the Ural (Butikov S.E., Gervasyev A.M., Glushkov L.A., Kamyshenko M.T., Olifer V.D., etc.), Krivoy Rog (Afanasyev I.I., Boshnyakov E.N., etc.) became famous , Neykov O.D., Logachev I.N., Minko V.A., Sheleketin A.V. and American (Khemeon V., Pring R.) calculating the localization of dust emissions using aspiration. Technical solutions developed on their basis in the field of designing aspiration systems are enshrined in a number of regulatory and scientific-methodological materials.

These methodological materials summarize the accumulated knowledge in the field of designing aspiration systems and centralized vacuum dust collection (CVA) systems. The use of the latter is expanding especially in production, where hydraulic flushing is unacceptable for technological and construction reasons. Intended for the training of environmental engineers, methodological materials complement the course “ Industrial ventilation"and provide for the development of practical skills among senior students of the specialty 05/17/09. These materials are aimed at ensuring that students are able to:

Determine the required performance of local suction pumps and CPU nozzles;

Select rational and reliable pipeline systems with minimal energy losses;

Determine the required power of the aspiration unit and select the appropriate draft means

And they knew:

The physical basis for calculating the performance of local suction stations;

The fundamental difference between the hydraulic calculation of central control systems and the AC air duct network;

Structural design of shelters for reloading units and CPU nozzles;

Principles for ensuring the reliability of AS and CPU operation;

Principles for selecting a fan and features of its operation for a specific pipeline system.

The guidelines are focused on solving two practical problems: “Calculation and selection of aspiration equipment (practical task No. 1), “Calculation and selection of equipment for a vacuum system for collecting dust and spills (practical task No. 2).”

The testing of these tasks was carried out in the autumn semester of 1994 in practical classes of groups AG-41 and AG-42, to whose students the compilers express gratitude for the inaccuracies and technical errors they identified. Careful study of materials by students Titov V.A., Seroshtan G.N., Eremina G.V. gave us grounds to make changes to the content and edition of the guidelines.

1. Calculation and selection of aspiration equipment

Purpose of the work: determination of the required performance of the aspiration installation servicing the system of aspiration shelters for loading areas of belt conveyors, selection of an air duct system, dust collector and fan.

The task includes:

A. Calculation of the productivity of local suction (aspiration volumes).

B. Calculation of the dispersed composition and concentration of dust in the aspirated air.

B. Selecting a dust collector.

D. Hydraulic calculation of the aspiration system.

D. Selection of a fan and an electric motor for it.

Initial data

(The numerical values ​​of the initial values ​​are determined by the number of option N. The values ​​​​for option N = 25 are indicated in parentheses).

1. Consumption of transported material

G m =143.5 – 4.3N, (G m =36 kg/s)

2. Particle density of bulk material

2700 + 40N, (=3700 kg/m 3).

3. Initial moisture content of the material

4.5 – 0.1 N, (%)

4. Geometric parameters of the transfer chute, (Figure 1):

h 1 =0.5+0.02N, ()

h 3 =1–0.02N,

5. Types of shelters for the loading area of ​​the conveyor belt:

0 – shelters with single walls (for even N),

D – shelters with double walls (for odd N),

Conveyor belt width B, mm;

1200 (for N=1…5); 1000 (for N= 6…10); 800 (for N= 11…15),

650 (for N = 16…20); 500 (for N= 21…26).

Sf – cross-sectional area of ​​the gutter.

Rice. 1. Aspiration of the transfer unit: 1 – upper conveyor; 2 – upper cover; 3 – transfer chute; 4 – lower shelter; 5 – aspiration funnel; 6 – side outer walls; 7 – side internal walls; 8 – rigid internal partition; 9 – conveyor belt; 10 – end outer walls; 11 – end inner wall; 12 – lower conveyor

Table 1. Geometric dimensions of the lower shelter, m

Table 2. Particle size distribution of the transported material

* z =100(1 – 0.15).

Table 3. Length of sections of the aspiration network

2. Calculation part 6

2.1. Calculation method 6

2.1.1. Calculation sequence 6

2.1.2. Determination of pressure loss in an air duct 7

2.1.3. Determination of pressure loss in the manifold 8

2.1.4. Calculation of dust collecting apparatus 9

2.1.5. Calculation of the material balance of the dust collection process 11

2.1.6. Selection of fan and electric motor 12

2.2. Calculation example 13

2.2.1. Aerodynamic calculation of the aspiration network (from local suction to the collector inclusive) 13

2.2.2. Linking the resistances of sections 19

2.2.3. Calculation of pressure loss in the manifold 22

2.2.4. Calculation of dust collecting apparatus 23

2.2.5. Calculation of sections 7 and 8 before installing fan 25

2.2.6. Selecting a fan and electric motor 28

2.2.7. Clarification of resistances of sections 7 and 8 29

2.2.8. Material balance of dust collection process 31

Bibliography 32

Appendix 1 33

Appendix 2 34

Appendix 3 35

Appendix 4 36

Appendix 5 37

Appendix 6 38

Appendix 7 39

Appendix 8 40

Appendix 9 41

Appendix 10 42

Appendix 11 43

Appendix 12 44

Appendix 13 46

Appendix 14 48

1. General Provisions

In wood processing processes on woodworking machines, a large amount of both large particles - production waste (shavings, chips, bark) and smaller ones (sawdust, dust) is formed. A feature of this technological process is the significant speed imparted to the resulting particles when the cutting tool acts on the material being processed, as well as the high intensity of dust formation. Therefore, almost all woodworking machines are equipped with exhaust devices, which are commonly called local suction.

A system that combines local suction, air ducts, a collector (a collection to which air ducts - branches are connected), a dust collecting apparatus and a fan is called aspiration system.

The set of air ducts - branches connected to the collector is called knot.

In woodworking areas equipped with machines, collectors of various designs are used (Fig. 1). The characteristics of some types of collectors are given in table. 1.

To move the generated waste (for example, from waste storage bunkers to the fuel bunkers of the boiler room), a pneumatic transport system is used; its difference from the aspiration system is that the functions of local suction are performed by the loading funnel.

The most important characteristic used in the calculations of aspiration and pneumatic transport systems is the mass concentration of dusty air (M, kg/kg). Mass concentration is the ratio of the amount of material being moved to the amount of air transporting it:

Rice. 1. Types of collectors:

a) vertical manifold with bottom outlet (drum)

b) vertical collector with an upper outlet (“chandelier”) c) horizontal collector

Table 1

kg/kg, (1)

Where G Σ n– total mass flow rate of transported material, kg/h;

L Σ – the total amount of air required to move the material (volume flow), m 3 /h;

ρ V– air density, kg/m3. At a temperature of 20°C and atmospheric pressure B = 101.3 kPa, ρ V = 1.21 kg/m3.

When designing aspiration systems, an important place is occupied by aerodynamic calculations, which consist in choosing the diameters of air ducts, selecting a collector, determining velocities in sections, calculating and subsequently linking pressure losses in sections, and determining the total resistance of the system.

Let us consider the fundamental aspiration transport and technological systems of construction industry enterprises. The composition of the equipment for the bulk raw materials acceptance line includes a hopper, a conveyor, a bucket elevator, and a conveyor. Dust-air flows are formed mainly in the following sections: bunker - conveyor, conveyor - elevator, elevator - gravity pipeline at the elevator - chain conveyor section. Accordingly, zones of increased and low blood pressure air.

In Fig. 2.3 shows a diagram of the connection to the aspiration system of the equipment of the soupy raw materials receiving area.

Air suction can be carried out in two ways: the first is to connect all places to the aspiration network high blood pressure: bunker, conveyor, elevator, chain conveyor; the second is to connect the hopper, shoe and elevator head, and conveyor to the aspiration network. With the second method, the length of the air ducts is significantly reduced, and the amount of dust entrained by the aspiration air duct is reduced, which makes the second method preferable.

For our example, the living area of ​​the grid above the receiving hopper should be kept to a minimum. Only those areas through which bulk material from vehicles enters the receiving hopper should be open. To reduce the contact area of ​​the falling flow of material with air and reduce the volume of ejected air, folding sealing shields should be used.

Fig. 2.3 Diagram of connection to the aspiration system of the equipment of the railway car unloading area: 1 - railway car; 2 - bunker; 3 – conveyor; 4 – elevator; 5 - chain conveyor; 6 - aspiration network; 7- sealing shields.

The volume of aspirated air from the receiving hopper is determined by the formula for the balance of air inflow and air flow

With a maximum mass flow of material of 100 t/h and a fall height of 2 m, see Table. 2.1 Le = 160 m³/h; vn - air speed in the holes, 0.2 m/s; Fn – leakage area of ​​the receiving hopper, 3 m²; Gm – volumetric mass of the material, 46 m³; t – unloading time, 180 s; we get:

La bun = 160 + ((0.2 * 3)*3600) + ((46 / 180)*3600) = 3240 m³/h

The values ​​of the volumes of aspirated air from the NTs-100 elevator (working and idle pipes) and the TSC-100 chain conveyor are obtained from regulatory documentation:

La no. work = 450 m³/h; La no. cold = 450 m³/h; La chain = 420 m³/h;

For the entire suction system:

La = 3240 + 450 + 450 + 420 = 4560 m³/h;

The pressure value in the aspiration pipe of the receiving hopper, taking into account the ejection pressure created bulk material with a fall height of 2m and a bulk tray is:

On bun = 50 + 50 = 100Pa

The pressure in each of the aspiration pipes of the elevator, taking into account the jet pressure in the discharge box of the conveyor, is:

At nor = 30 + 50 = 80Pa

The pressure in the aspiration pipe of the chain conveyor, taking into account the ejection pressure in inclined gravity flow up to 2 m and vacuum in the hopper, is:

On flail = 50 + 50 + 30 = 130Pa

Having received the initial data and configured the aspiration system, we will perform an aerodynamic calculation of the system performance

La = 4560 m³/h; see fig. 2.3, which we display on the workshop plan in the following sequence:

1. Air ducts and other elements of the aspiration system are drawn onto the floor plan, followed by the construction of a spatial (axonometric) aspiration diagram.

2. The main direction of air movement is selected. The main direction is considered to be the most extended or loaded direction from the fan to the starting point of the first section of the system.

3. The system is divided into sections with constant flow air, sections are numbered starting from the one furthest from the fan, first along the main line, and then along the branches. Determine the length of sections and air flow and enter these values ​​into Table 2.3, columns 1, 2, 3.

4. We preset the approximate air speed v or, m/s, in section 1 of the air duct (depending on the air speed for a given dust, see Table 2.4). Based on the planning requirements, we take the shape of the air duct and the material from which it is made (round, galvanized steel). The pressure loss in the chain conveyor connected to section 1 is entered in the table. 2.3 first line. To determine the pressure loss in section 1, we connect with a straight line according to the nomogram in Fig. 2.5 points Lchain=420 m³/h and v=10.5 m/s at the intersection of this line with the scale D we find the nearest smaller recommended diameter D = 125 mm, values v=10.5 m/s, Hd =67 Pa, λ/D=0.18 are entered in columns 3, 6, 8.

5. We sum up the local resistance coefficients on the section (tees, bends, etc.) selected by . We write the obtained result Σ ζ in column 5.

6. We perform multiplication, ( 1 * λ/D) fill in column 9, addition ( 1 * λ/D + Σ ζ) fill in column 10. Column 11 (total losses in the section) is found as the product of the values ​​​​recorded in columns 6 and 10. In column 12 we write the sum of the total losses in section 1 and pressure losses in the chain conveyor.

We carry out calculations of the remaining main sections in the same way.

7. At the end of the calculations, we sum up the obtained values ​​and obtain the total pressure loss in the network, which serves as a criterion for selecting a fan.

8. Having calculated the pressure loss along the main line, we proceed to calculate the pressure loss on the branches. When calculating which it is necessary to link, the discrepancy is allowed no more than 10%.

9. There are two ways to increase pressure losses in branches. The first method is to install additional local resistance (valve, diaphragm, washer) in the branch. The second method is to reduce the diameter of the branch.

In the example under consideration, the resistance of the 7th section should be increased by Hc = 237 - 186.7 = 50.3 Pa, and the 8th by - Hc = 373 - 187.7 = 185.3 Pa, and the 9th by - Ns = 460 - 157.8 = 302.2 Pa. In areas 7 and 8 this can be done by installing additional local resistance because The pipe diameter is already 125 mm. The value of the resistance coefficient of the diaphragm installed in section 7 is determined by the expression:

ζd7 = Ns / Nd7 = 50.3 / 74.1 = 0.68 (2.10)

According to this value in Fig. 2.4 we determine the depth of immersion of the diaphragm into the air duct to its diameter - a / D = 0.36, with D = 125 mm a = 43.75 mm. Similarly for sections 8 and 9: ζд8 = Нс / Нд8 = 185.3 / 74.1 = 2.5 according to Fig. 5.3 we determine - a / D = 0.53, with D = 125 mm a = 66.3 mm; ζd9 = Ns / Nd9 = 302.2 74.1 = 4.1 according to Fig. 2.3 we determine - a / D = 0.59, with D = 315 mm a = 186 mm;

Rice. 2.4 Single-sided diaphragm (a) and double scale for calculating dimensions (b)

Fig. 2.5 Nomogram by A.V. Panchenko for calculating air ducts.

Table 2.3

Aerodynamic calculation of air ducts.

Main sections

Table 2.4 Values ​​for the design of aspiration and pneumatic transport systems