Calculation of basic parameters for pneumatic conveying

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Calculation of basic system parameters 　　　　1. Equivalent length of ash conveying pipes, Leg The total equivalent length of the ash conveying pipes is given by: Leg=L+H+∑nLr (m)　　　(5-19) 　　　　2. Ash-to-air ratio μ Sharing information, improving technical standards, and optimizing project quality%\)p)o"\1q8`*Q4i"g)a The average mixing ratio can be calculated using the following formula, based on the selected capacity of the air compressor and the output of the silo pump: www.eppbbs.com&z+}&^!I"M1k2M7V 　　　　　　　μ=φGhX103/　　　　 (kg/kg)　　(5-20) 　　　　　　　　　　Gh=ψγhνp (t/silo) Energy and Environment Protection Forum+u w6o;v$?+G8M+s (5-21) Where ;www.eppbbs.com0T+b1w8F.?*j6I'P;W1`(f Since both single-silo and double-silo pumps operate intermittently, the amount of air required by the system must be determined based on the air consumption per operating cycle of the silo pump, and this value is then converted into an average air consumption per minute. That is: Volume flow rate Qa=φGhX103/　(m3/min)　　　(5-22) Energy and Environment Protection Forum6o5B9x7L8X#_!z |*?+R Mass flow rate Ga=Qaγa=16.67 Gm/μ 　　　(kg/min)　　　　 (5-23) Energy and Environment Protection Forum%z2x;|1www.eppbbs.com6I6G2b4k9W7d The distance over which the ash is conveyed in a positive-pressure pneumatic ash removal system using silo pumps is generally quite long. To ensure the safe and efficient operation of the system, it is necessary to increase the diameter of the pipes along the conveying pipeline section by section. Usually, 2–3 different pipe diameters are used so that the conveying speed in each section remains within the recommended range. Based on practical experience, the recommended conveying speeds for each section are as follows: Speed at the beginning of the pipeline: νb =10-12m/s； 　　　 Velocity at the ends of the upper and middle sections of the pipeline: νe=15-20 m/s ； Energy and Environmental Protection Forum!r-s$]/J.D8g;W'X 　　　　Velocity at the end of the downstream pipeline: νe=15-25 m/s. Share information, improve technical skills, and optimize project quality. 3I&z,r0{:F!w&D)\5? The actual velocity at the end of the pipe section, νe, can be calculated using the following formula: νe = 0.0212Qe/D2 (m/s) (5-25). Qe = (paTe/peTa).Qm (m3/s) (5-26). In these formulas, Qe represents the volumetric flow rate at the end of the pipe section, in m3/min; pe is the absolute pressure at that end, in Pa; and Te is the temperature at that end, in K ； 　　　　　　　　　　　　　pa—local atmospheric pressure, Pa ； Share information, improve technical skills, and optimize project quality’`9~1U:K(b(d 　　　　　　　　　　　　　Ta—Average local atmospheric temperature, K 　　　　　　　　　　　　　D—Inner diameter of the pipeline, m. Share information, improve technical skills, and optimize project quality/h6K7F-}'x2~ Energy and Environmental Protection Forum, o4Z'{.W;_,g8O5G%{ Calculation of system output Gm Author: qlss Source: China Pneumatic Conveying Network Update date: July 20, 2005 Energy and Environmental Protection Forum&}:@)S6W1y"Q:n (I) System output Gm 　　　　　　　The output of pneumatic ash removal equipment can be determined based on the system’s maximum conveying capacity (taking into account factors such as the maintenance time required for the conveying system and equipment). For silo pump systems, during calculation, based on the designed flow rate Gms and the pipeline length, a specific model of silo pump can be initially selected; thereafter, the system power Gm of that silo pump is determined to see whether it can meet the transportation requirements, that is, Gm ≥ Gms. 　　　　Single-chamber pump: Gm=60ψγhνp/(t1+t2) (t/h) (5-16) Share information, improve technical skills, and optimize project quality. 8S0U&S;^#h.O$c.{)z7@ Double-chamber pump: Gm=60ψγhνp/(t2+t3) (t/h) (5-17) t3=φX(νb/Qm)XX (min) (5-18) Where ψ is the filling coefficient of the pump chamber, usually taken as 0.8 ； 　　　 γh—is the bulk density of ash, which can be approximated as 0.7~0.8 t/m3 ； 　　　νp—geometric volume of the silo pump, in m3 ； 　　　t1—Time required to fill Bin 1 with ash; depends on the type and capacity of the feeding equipment, in minutes. t2—Time required to blow out the ash from Bin 1; mainly depends on the length of the conveying pipes, in minutes. Energy and Environment Forum X8u'J6c8n7W.X t3—Time for the pressure in the bin pump to recover, in minutes ； ;\%@#q*b;](U8X 　　　　　　　　　 φ—leakage coefficient of the gas supply system, generally taken as 1.1-1.2 Energy and Environmental Protection Forum, N/B+x,X8V1y2c8C;w 　　　　　　　　　　　νb—total volume of gas stored in the supply system, in m3 ； Energy and Environmental Protection Forum 4E)Z1|:C6v*x)V 　　　　　　　　　　　Qm—The free air flow rate of the air compressor, in m3/min. Sharing information helps to improve technical skills and optimize project quality. R5p$_%l5M o5k 　　　　　　　　　　　po—The pressure when the silo pump starts cleaning, in Pa. 　　　　　　　　　　　pc—The pressure when the silo pump stops cleaning, in Pa. Energy and Environmental Protection Forum*a+v5O:B)n7s:J 　　　　　　　　　　　pa—The local atmospheric pressure, in Pa ； 　　　　　　　　　　　ta—average local atmospheric temperature, °C 　　　　　　　　　　　t—temperature of the compressed air supply, °C www.eppbbs.com/Z:u1~ Pressure loss △p in the ash removal system Energy and Environmental Protection Forum $M)S2B)A*_!J;U:P#Z Author: qlss Source: China Pneumatic Conveying Network Update date: July 20, 2005 Pressure loss △p in the ash removal system The pressure loss in a positive-pressure pneumatic ash removal system using silo pumps is calculated segment by segment, starting from the end of the entire pipeline (i.e., the interface where the ash is discharged into the ash storage area) and moving towards the beginning of the pipeline. The pressure loss in the positive-pressure pneumatic ash removal system consists of the following components. Share information, improve technical skills, and optimize project quality &z8C3l"H*L0b9W 　1. Pipeline pressure loss △p1 Energy and Environmental Protection Forum %c+z:q"x!D&U9R2v 　The pressure loss in a delivery pipeline should be the sum of the pressure losses in horizontal, vertical, inclined pipelines, as well as pipeline accessories. To simplify the calculations, it is generally possible to convert each section into an equivalent length of horizontal pipe, resulting in the following calculation formula: Energy and Environmental Protection Forum-~*|,E5f;i%q8E △p1={1/2－pe}(1＋Kμ) (Pa) (5-27) www.eppbbs.com7~$R5k#O'?&C Where pe represents the absolute pressure at the end of the pipe section, in Pa; for the last pipe section, pe is the pressure at the inlet interface ； Energy and Environmental Protection Forum (o;e8Q/P+G A λa— The coefficient of air friction loss for the pipe section, calculated using equation (5-9). Leq— The equivalent length of the pipe section, in meters, determined using formula (5-19) as well as Tables 5-1 and 5-2 ； 　D—Internal diameter of the pipe in the pipe segment, m ； 　γe—Air specific weight at the end of the pipe section, kgf/m3 νe—Flow velocity at the end of the pipe section, m/s ； 　μ—is the ash-to-gas mixture ratio, calculated using equation (5-20), in kg (ash)/kg (gas) ； www.eppbbs.com%h$P*^;c;j(W(O _;l 　K—two-phase flow coefficient, which can generally be determined through experiments or selected using the data provided in Table 5-3. Energy and Environmental Protection Forum 0a#u’R9\9| 2. Pressure loss △pp in conveying equipment: Sharing information, improving technical skills, and optimizing project quality, e/D,b’y:i4M,W. The pressure loss within top-entry silo pumps is shown in Table 5–5; the pressure losses for other types of silo pumps can be determined by referring to this table. 　　Table 5–5 Pressure loss table for the above-mentioned silo pumps. Flow rate of the silo pump (m3/min): 20–40, >40. Pressure loss Δpp (Pa): 6000–12000, 12000–15000. Energy and Environment Forum (m7N, L:~3Z-T$q, C7w). 3. Pressure loss Δpac caused by the acceleration of ash particles. The pressure loss resulting from the acceleration of ash particles at the feeding point, at points where the pipe diameter changes, and after bends can be calculated using equation (5–13). 6\0m#T/`4k,www.eppbbs.com5@!I%b:H"L9c"k)Z)d 　5. The pressure loss △pi9t.?"|%n9]6F0Y2D"?'@0W8N)A for bag filters can generally be determined using the data on pressure loss provided by the manufacturer. Energy and Environmental Protection Forum.v"b*Y)S G R 　　　Based on the above considerations, the formula for calculating the pressure loss in a positive-pressure pneumatic ash removal system is as follows: 　△p =∑△p1 +△pp +△pac +△p0 +△pi　　(Pa)　　　　(5—29) 　　　Where ∑△p1 represents the total pressure loss across all the sections of the pipeline, in Pa. (Energy and Environmental Protection Forum%U&u e9{'_+E Calculation of the output capacity of the negative-pressure ash removal system Gm &S#V+F6C A7K"G3B Author: qlss Source: China Pneumatic Conveying Network Last updated: July 20, 2005 I. Calculation of the negative-pressure ash removal system $k;^/]3G$j$@6W"I8?+P7I 　　　　　　　　　　　　　　　Table 5-4　　　　　　　Relationship between system output and pipe diameter Pipe diameter (mm) DN150 DN125 DN150 DN200 DN250 Energy and Environmental Protection Forum6Q#K)E0c&_;f9h(`'z&O System output (t/h) 5-8 8-10 10-15 15-40 40-60 Sharing information to improve technical skills and optimize project quality X3.6/　　 (t/h)　　　　(5-15) 　　　　　Where　　　　　　　f—is the friction coefficient ； Energy and Environmental Protection Forum, p8t*z;V2O+Y$M*~"c1h 　　　　　　　　　　　　　　　g—acceleration due to gravity, 9.81 m/s2. Sharing information, improving technical skills, and optimizing project quality +H9~:K1{'I 　　　　　　　　　　　　　　　H—vertical rise, in meters ； 　　　　　　　　　　　　　　　Lf—horizontal transport distance, m ； 　　　　　　　　　　　　　　　k—constant moisture index, which can be set at 1.2 　　　　　　　　　　　　　 N—number of 90° elbows; when the elbow angle is less than 90°, it is calculated as if it were a 90° elbow. www.eppbbs.com*L$o4P+x3d.c.^ 　　　　　　　　　　　　　　　p1—air pressure at the inlet of the negative-pressure device, in Pa (absolute) 　　　　　　　　　　　　　　　P2—air pressure at the outlet of the negative-pressure device, in Pa (absolute) 　　　　　　　　　　　　　　　Q—air flow rate at the inlet of the negative-pressure device, in m3/S www.eppbbs.com*M,K&@-D6d.`!g&m 　　　　　　　　　　　　　　　v1—specific volume of air at the inlet of the negative-pressure device, in m3/kg ； Share information, improve technical skills, and optimize project quality. 67t#l 　　　　　　　　　　　　　　　w—Average flow velocity of the pipeline, in m/s. Economic Analysis of Pneumatic Conveying Systems Energy and Environmental Protection Forum+h8P!m&L-L9g3u!` Author: qlss Source: China Pneumatic Conveying Network Date of update: July 24, 2005 www.eppbbs.com,`:X!C"B \(f When designing a pneumatic ash removal system, it is first necessary to ensure that the intended conveying tasks can be accomplished. At the same time, it is important to decide appropriately on the type and capacity of equipment to be used, as well as other related factors. During design, one should not focus solely on the cost of the equipment; rather, it is crucial to take into account the impact of the material’s properties on quality, the volume and distance of conveyance, the route taken for conveyance, as well as the difficulties and costs associated with operation and management. For example, in some cases, although all types of equipment seem suitable for pneumatic conveying, such methods cannot be used due to reasons like high moisture content or stickiness of the material. In such situations, even if mechanical conveying equipment is more expensive, it must still be chosen as the preferred method. There are also situations where, when transporting certain materials – for example, limestone powder to the feed hopper in front of a circulating fluidized bed boiler – pneumatic conveying requires a high amount of power, which may seem to result in higher operating costs. However, from the perspective of system efficiency or production technology, pneumatic conveying is still the better option. Under what circumstances is it more economical to use one method over another? Generally speaking, mechanical transport is advantageous for short-distance transportation ； Conversely, for longer-distance transportation, although pneumatic conveying systems are less advantageous in terms of the power required, they are often more cost-effective in terms of equipment expenses. Equipment costs, required power, and operating expenses vary greatly depending on surrounding conditions, so it is not possible to make general comparisons. Additionally, it should be noted that these values also change significantly depending on the specifics of various platform supports and auxiliary equipment. In summary, when designing a pneumatic ash removal system, it is necessary to select the most suitable conveying system and corresponding equipment based on the specific conditions of the project, through a comprehensive technical and economic comparison. If the system’s delivery capacity and distance are fixed, the economic efficiency of the system generally depends on the mixture ratio of ash and air being transported. In terms of equipment energy consumption, the power required by the compression (extraction) equipment is proportional to the product of the system pressure and the air flow rate. If the ratio of ash to gas is increased, the amount of air required for transportation can be reduced. Under conditions where the transportation speed remains constant, the amount of air needed is proportional to the square of the pipe diameter, that is, Q∝D2. Meanwhile, the system pressure, or the resistance in the transportation pipes, is inversely proportional to the inner diameter of the pipes, that is, P∝1/D; thus, the ratio of ash to gas does not increase in a direct proportionate manner. Therefore, increasing the ratio of ash to gas and reducing the amount of air used is highly beneficial for lowering the energy consumption of the pumping equipment. Secondly, in terms of the initial investment required for the system, an increase in the ash-to-gas ratio allows for a reduction in the size of the equipment and the inner diameter of the transportation pipes, as well as lower costs for supports and installation. Hence, the effect of reducing the initial investment in the system is also evident. 　　　The larger the gray gas ratio μ, the more favorable it is for increasing the transport capacity, and it will obviously also improve economic efficiency. However, if the ratio of gray gas is too high, blockages may occur at the same airflow velocity, and the conveying pressure also increases. In negative-pressure and low-positive-pressure pneumatic conveying systems, this could exceed the suction pressure or exhaust pressure allowed by the compression machinery. Therefore, the value of the ash-to-gas ratio is constrained by factors such as the physical properties of the material, the conveying method, and the conveying conditions. Especially in positive pressure pneumatic conveying systems, the ash-to-air ratio is naturally more constrained by factors such as the size and design of the silo pump itself, the inner diameter and length of the conveying pipes, the number of elbows, and the amount of air used. When performing design calculations, it is necessary to take into account the conveying conditions and refer to various examples when selecting the value for the ash-to-gas ratio. The general range of values that can be adopted is shown in Table 5-8. (Energy and Environmental Protection Forum) V9y*c9a(A(j%i8E Table 5-8 Values of the ash-to-gas ratio μ Conveying method μ www.eppbbs.com2z:^*h'w*G*t *(L-L Negative pressure: low vacuum, less than 10 www.eppbbs.com"b0T&^,W'Y9L(h,S!M"N High vacuum: 10–20 Energy and Environmental Protection Forum 5J;c%5Z$j As can be seen from the table above, after comprehensive comparison, a high-concentration dense-phase pneumatic conveying system should be preferred whenever possible. Energy and Environment Forum: p*p.h'C3r6Z Table 5–9 provides an example of a German company. As can be seen from the table, compared with mechanical methods, the pneumatic ash removal system has higher power consumption; the operating costs are similar, but the equipment cost is much lower. However, in China, this result can only be achieved once domestic pneumatic ash removal devices are developed. 　　　　　　　　　　　　　　　　　　Table 5-9　　　　　　　　　Economic comparison of conveying methods www.eppbbs.com3i5^/^-}2z-s#Z.W+L Method Main equipment Equipment cost (marks) Energy and Environment Forum5|#`!w%D*M Power consumption Operating cost (marks/t) (Kw·h) (marks/t) (1) Mechanical ash removal system Screw conveyor – Bucket elevator – Belt conveyor (including platform supports and walkways) + Ash removal device 430,000 70 0.08 0.40 Energy and Environment Forum5f7i(L4R+l0] (2) Combination of mechanical ash removal and air chutes Screw conveyor – (Bucket elevator – Air chutes) in 2 sections (including platform supports) + Dust removal device 230,000 50 0.06 0.23 (3) Pneumatic ash removal system Silo pump – Conveying pipes (including dry platform supports) – Cyclone separator + Dust removal device, including air compressor 150,000 80 180* 0.09+0.2 Share information, improve technical skills, and optimize project quality 5b:s/z.?(P8M0U 0.30**&`(X0m5L"a"z(Y 0.41 Energy and Environment Forum’_*s;p1~;L8F6M"t&K1K.` * Cement conveying capacity: 60 t/h; conveying distance: 300 m. www.eppbbs.com8}(q#y!r2X,u%o.U(I#w 　　　　　** Assuming that 60 m3 of air is required per ton of cement to be transported, and that air at a pressure of 0.2 MPa requires 0.05 KW·h of energy per m3, the total energy consumption is 180 KW·h. The cost of electricity used is 0.3 marks per ton. Energy Conservation Forum%o5_8b4I(u+G2G’y9m3K,j;W#p(c 　　　　　Table 5–10 provides examples comparing the diameter of the conveying pipes and the power consumption required when transporting materials over distances of 30, 150, and 300 meters at a rate of 10/h, using different methods. www.eppbbs.com%E2E'\5d3F+^9]5D+T High-pressure conveying method, Low-pressure conveying method, Negative-pressure conveying method. Transport volume (t/h): 10, 10, 10; 10, 10, 10; 10, 10, 10. Transport distance (m): 30, 150, 300; 30, 150, 300; 30, 150, 300. www.eppbbs.com)Q:M&K%G;v*c0c1q1@ Pipe diameter (inches): 2, 2X(1/2), 3, 4, 7, 10; 4, 8, 10. Energy Conservation Forum)O0g8e7u4P)S Compressors used: Air compressors, Roots blowers, Roots blowers. Energy Conservation Forum4n;U5[-V)}5b-\&s Power (KW): 19, 30, 37; 11, 30, 45; 15, 37, 60. Energy Conservation Forum4E5O;_:Y3R!R8j+z Power ratio ①: 146, 100, 100, 100, 107, 127, 131, 130, 167. 　　　　　　　　　　　　①This value represents the comparison with other methods over the same transport distance.