CN201242338Y - Drying line for paper stuff molding based on variable-frequency control technology - Google Patents

Abstract

The utility model discloses a drying line of paper mould based on the frequency control technique, which is characterized in that each of drying sections is provided with a circulating fan, each of the circulating fans is connected with a frequency-changer which is specially used for the fans, except for circulating hot air in a dry oven, the circulating fan is characterized in that an air inlet thereof is further connected with a hot air pipe which is leaded out from an air heating furnace, an electric air door is arranged between the inlets of the hot air pipe and the circulating fan, the drying line is an efficient-optimized automatic control system, which models complex objects according to the drying characteristics of the paper mould and the size and the weight of different wet ground paper, wherein the process control technique, the alternating current frequency control technique and the modern detecting technique are adopted to carry out the frequency conversion stepless speed change control to the circulating fan, the electric air door, a dehumidifying fan and a carrier-chain drive motor according to temperature and humidity signals which are detected on the spot, and the operation speed of a conveyer belt in a drying channel, the work temperature in each stage dryer, the hot air quantity and the discharging of vapor are reasonably adjusted, a reasonable drying curve is formed, the deformation of products is reduced as much as possible, the wastage of electrical energy and heat energy are saved in maximum, the drying speed is improved, the yield of the drying production line is increased, and the optimum control is realized.

Description

A kind of paper pulp molding drying line based on variable-frequency control technique

Technical field

The utility model relates to a kind of paper pulp molding drying line based on variable-frequency control technique.

Background technology

Moulded paper pulp product is considered to the best substitute of EPS white pollution packaging product, is called as " green package of 21 century ".The technological process of production of moulded paper pulp product is: pulping, vacuum forming, oven dry, hot pressing integer.At first, waste paper group or sole plales are combined with a certain proportion of water, drop into hydrabrusher, utilize hydraulic action to blend decomposition at a high speed, thereby the paper fiber is mixed in the water, formation meets necessarily required slurry.By vacuum adsorption method, slurry is evenly distributed on the mould again, further dehydration, the demoulding, l Water Paper base basic forming at this moment.But the l Water Paper base after the moulding contains than high-moisture, needs drying to remove.Finalized the design for making moulded paper pulp product have better shockproof properties and cleaner and tidier smooth outward appearance, dried goods can be placed on the reshaper mould of HTHP, so far the production process of moulded paper pulp product is all finished.Paper mould industry is in existing more than the 80 year history of some developed countries, and the tool certain scale.And China's paper mould industrial development is slow relatively.External paper mould development characteristic is: applied range; The goods design standardization; The automaticity height; The energy utilization rate height is saved the labour.But restraining factors such as it is not high that China's product line of pulp molding ubiquity automaticity, and energy waste is big, and the product pass rate is low.Especially on the paper pulp molding drying operation, more outstanding to above-mentioned restraining factors performance.The oven dry cost of moulded paper pulp product accounts for the 30%-40% of whole production cost.And the hot air convection drying is the drying mode that generally adopts both at home and abroad.At present, drying production line both domestic and external all adopts central heating, the structural form of segmentation oven dry, by combustor or other thermal source to the combustion chamber central heating, main drying tunnel adopts the drying section form, and the circulating fan by every section drying tunnel is transported to hot blast drying section and continues circulation from the combustion chamber, the chain type conveyer belt passes in the middle of drying tunnel, hot blast blows by the wet goods of the paper pulp of wind hole on conveyer belt on the gas distribution grid, product is carried out stage drying, and the moisture in the drying tunnel is taken away by the dehumidifier blower fan.

Usually the capacity of the circulating fan (dehumidifier blower fan) of every section drying tunnel is to require and design according to maximum that system needs, yet (according to the different size and the quality of product) in actual applications, system worked under design capacity in most of times.When needs lower to be carried air quantity, traditional control method was to install air door additional in the exit of circulating fan (dehumidifier blower fan), promptly changed the characteristic method of pipe-line system and regulated with turning down the local resistance of air door increasing system.This method is simply effective, but has had a strong impact on the efficient of system and wasted most electric energy and heat energy.By Hydrodynamics Theory as can be known, the conveying air quantity of blower fan is directly proportional with the first power of the rotation speed n of blower fan, and the torque of blower fan is directly proportional with the quadratic power of n, and its power then is directly proportional with the cube of n.Therefore, when fan delivery drops to 80% by 100%, do not adopt the method that turns down air door and adopt the stator frequency of supply that changes threephase asynchronous, and change the method for the running speed of blower fan, then effectively the blower fan power consumption is dropped to 51.2%, thus saves energy 49.7%.And the adjusting of traditional drying line throttle opening is manually-operated, it can not in time make adaptive adjusting according to the variation of systematic parameter, also not do not set out the optimal working curve at the drying property of different drying stages and carry out segmentation control at moulded paper pulp product, system exists serious randomness and blindness, cause drying time too short or long, Product Variant is serious, and energy waste is big, drying efficiency is low, restraining factors such as percent defective height.

Summary of the invention

A kind of paper pulp molding drying line based on variable-frequency control technique that the utility model provides comprises combustor, hot-blast stove, baking oven, circulating fan, dehumidifier blower fan, conveyer belt, and combustor connects hot-blast stove; Above-mentioned baking oven adopts frame structure, and conveyer belt is installed in oven interior, and baking oven length and width determine that according to output baking oven is divided into several drying sections; Each drying section is equipped with circulating fan, each circulating fan connects blower fan tailored version frequency converter, the hot-air of circulating fan in the circulation baking oven, the circulating fan air inlet also is connected with the warm-air pipe of being drawn by hot-blast stove, between the air inlet of warm-air pipe and circulating fan MOD is housed, MOD is connected with frequency converter; The circulating fan air outlet is connected with exhaust duct, and exhaust duct is directly sent to hot blast on the conveyer belt; The dehumidifier blower fan is housed in baking oven, the dehumidifier blower fan connects blower fan tailored version frequency converter, the mounting temperature sensor respectively at the air outlet place of the central authorities of each drying section of drying line and warm-air pipe, air inlet at the dehumidifier blower fan is installed humidity sensor, at the air outlet mounting temperature sensor of dehumidifier blower fan; The control of drying line is finished by programmable logic controller (PLC) PLC, and PLC passes through to receive the data of each sensor, and compares with the optimal value of setting, and draws regulated quantity and sends control instruction to each frequency converter; Conveyer belt is equipped with driving motor, and driving motor connects frequency converter, and worm type of reduction gearing is positioned between driving motor and the conveyer belt; The drying line console is equipped with the touch-screen of man-machine interface.

The above-mentioned frequency converter that is connected with circulating fan is the blower fan tailored version frequency converter FR-740-5.5k-CHT (1) that Mitsubishi is produced, and it is connected with PLC by the FX2N-485-BD module, realizes the adjusting to the circulating fan rotating speed.

The above-mentioned frequency converter that is connected with the dehumidifier blower fan is the blower fan tailored version frequency converter FR-740-3.7k-CHT (1) that Mitsubishi is produced, and it is connected with PLC by the FX2N-485-BD module, realizes the PID of dehumidifier rotation speed of fan is regulated.

The above-mentioned frequency converter that is connected with air door is the blower fan tailored version frequency converter FR-740-1.5k-CHT (1) that Mitsubishi is produced, and it is connected with PLC by the FX2N-485-BD module, realizes the PID of throttle opening is regulated.

The above-mentioned frequency converter that is connected with the carrier chain driving motor is the blower fan tailored version frequency converter FR-740-1.5k-CHT (1) that Mitsubishi is produced, and it is connected with PLC by the FX2N-485-BD module, realizes the adjusting to the carrier chain transmission speed.

The FX2N-16MR PLC that above-mentioned PLC selects for use Mitsubishi to produce, PLC passes through the FX2N-8AD module from temperature sensor and humidity sensor receiving real-time data, and compare with the optimal value of setting by paper pulp molding drying specificity analysis and the HMI that draws at the theoretical model of percolation drying line, be connected thereof by RS-422, draw regulated quantity and send control instruction to each frequency converter, thereby reach the effect of controlling rotation speed of fan, throttle opening and conveyer belt transporting velocity by the FX2N-485-BD module.

The said temperature sensor is connected with PLC by the FX2N-8AD module with humidity sensor, and detected data are sent to PLC

Above-mentioned HMI is the A956WGOT that Mitsubishi is produced, and it realizes the no-protocol communication by RS-422 and PLC.

Use the production craft step of above-mentioned drying line as follows:

1), draws correlation formula about the important parameter of each oven dry section of paper pulp molding drying line according to the paper pulp molding drying specificity analysis and at the theoretical model of percolation drying line;

2) according to planned production output, calculate the drying line length and the segmentation baking oven number ratio that distributes, i.e. the number ratio of constant rate drying period and falling rate drying period segmentation baking oven, and draw the working speed and the operating frequency of conveyer belt motor;

3) single product to be dried is carried out drying experiment, draw the drying process temperature that optimum running parameter comprises constant rate drying period and falling rate drying period, air quantity, humidity;

4) with above-mentioned steps 1) and 2) the drying process parameter that draws is input to PLC by touch-screen HMI;

5) start drying line by touch-screen and move automatically, product to be dried is dropped into drying line, produce beginning;

6) temperature sensor of drying section and humidity sensor are gathered the manufacturing parameter of drying line in real time, and by the FX2N-4AD module analog quantity are transformed into digital quantity and pass to PLC;

7) PLC passes to each digital quantity correspondence by the communication of RS-485 no-protocol the MOD frequency converter and the dehumidifier fan frequency converter of each drying section;

8) the inner integrated PID of the frequency converter of each MOD module of adjusting is started working, it can compare according to real time temperature and the default technological temperature that the temperature sensor that is installed in drying section central authorities collects, and of the input of their error amount as the PID controller, and error be multiply by proportionality constant, the integration of error multiply by integral constant, the differential of error multiply by derivative constant, and their addition, thereby obtain the output of PID controller, then the result is given the frequency converter of MOD, thereby regulate the frequency of supply or the rotating operation of MOD, reach the purpose of control throttle opening, thereby the feeding ratio of control changes in temperature wind realizes the purpose that hot blast temperature is controlled in the segmentation baking oven; Proportionality constant wherein, integral constant, derivative constant is determined by test;

9) step 7 in like manner, the inner integrated PID of the frequency converter of the dehumidifier blower fan module of adjusting is started working, real-time humidity that it can collect according to humidity sensor in the baking oven and default technology humidity ratio are, and of the input of their error amount as the PID controller, and error be multiply by proportionality constant, the integration of error multiply by integral constant, the differential of error multiply by derivative constant, and their addition, thereby obtain the output of PID controller, then the result is given the frequency converter of dehumidifier blower fan, thereby regulate the frequency of supply of motor, reach the step-less adjustment of the exhausting amount of dehumidifier blower fan, guarantee that humidity is in the technological requirement scope in the baking oven; Proportionality constant wherein, integral constant, derivative constant is determined by test;

10) circulating fan according to formula (1-23) drying section passes through the frequency converter long-term work in step 2 and 3 operating frequencies of setting;

11) repeating step 5)～9), make drying line stably be operated in the optimum process curve.

The utility model is according to the drying mechanism of moulded paper pulp product, analysis contains the drying property of wet porous media at different drying stages, and according to waiting to dry product size and weight, adopt ac variable speed technology and modern detecting, temperature according to the scene detection, moisture signal, to circulating fan, MOD, the dehumidifier blower fan, the control of carrier chain driving motor stepless frequency control realizes the control of drying line segmentation temperature automatically, air quantity control and humidity control, and adjust the linear velocity of drying line conveyor chain automatically, make drying production line be operated in best operating point, effectively saves energy loss is improved the quality of products and the production efficiency of drying line.

The optimal control method that the utility model is produced the critical process process with flow process is applied to paper pulp molding drying technology, to realize optimal control, cuts down the consumption of energy, and enhances productivity.The energy conservation of research and exploitation paper mould industry baking operation and dispatching technique, the energy-saving and cost-reducing optimization running technology of emphasis production process are implemented energy-saving and cost-reducing skill upgrading and technological innovation, can significantly reduce the energy consumption and the material consumption of process industry industry.

Description of drawings

Fig. 1 is the outline drawing of drying line.

Wherein 1 is circulating fan, the 2nd, and hot-blast stove, the 3rd, combustor, the 4th, baking oven, the 5th, dehumidifier blower fan, the 6th, conveyer belt.

Fig. 2 is drying process figure.

Fig. 3 is a wherein schematic diagram of optimal control process.

Fig. 4 is the optimal control block diagram.

Fig. 5 is the drying curve figure of paper mould l Water Paper base.

Wherein AB represents warm-up phase, and BC represents constant rate period, and CD represents falling-rate period.

The specific embodiment

Moulded paper pulp product is containing higher moisture (about 70%) after the moulding, need to remove through baking operation, and the water content of dry back finished product is about 10%-15%.Water existence form in hygrometric state paper fiber has three kinds: in conjunction with water, adsorbed water and free water, and the drying purpose of moulded paper pulp product be exactly to remove wherein in conjunction with water and adsorbed water.Paper pulp moulding product belongs to and contains wet porous media, its drying property more complicated, and total dry run can be divided into three phases: preheating and drying, constant rate of drying, falling-rate periods of drying.The common preheating and drying stage holds time shorter, can ignore.And at constant rate drying period, the l Water Paper base absorbs heat from drying medium (hot-air), make internal moisture under barometric gradient to external diffusion, and surface moisture just flashes to steam, is taken away by drying medium.At this moment the water content of l Water Paper base is still many, the surface evaporation of l Water Paper base how much moisture, inner how much moisture that just replenishes, rate of drying is equal to the evaporation rate of water at Free Surface, basically rate of drying is a constant, and is linear from moisture and time that the l Water Paper base is taken away.When evaporation process slowly is deep into material inside, l Water Paper base internal moisture diffusion velocity begins to enter falling rate drying period less than diffusion into the surface speed, the material surface begins to have dry spot to occur, and the drying process is carried out in material inside, and whole material can be divided into does the district, evaporating area and wet district three parts.At this moment, the outside translational speed of material internal moisture is far fewer than the outside evaporation rate of surface moisture, the rate of drying of moulded paper pulp product is being not a constant, its rate of drying depends on the inner character of material, the slope of its drying curve reduces gradually along with increasing progressively of time, and drying curve as shown in Figure 5.Under general condition, moulded paper pulp product thickness than long and wide (generally greater than 10cm), can be considered infinitely great dull and stereotyped all at 2mm-4mm.According to infinitely great dull and stereotyped mathematical solution in Soret coefficient=0 o'clock, obtain the rate of drying expression formula of constant rate drying period

$\frac{\mathrm{dM}}{\mathrm{d\τ}}=\frac{\mathrm{\α}}{{\mathrm{\ρ\γ}}_{0}R}[{\stackrel{\‾}{t}}_c-{\stackrel{\‾}{t}}_{\left(\mathrm{\τ}\right)}]---(1-1)$

And the speed expression formula of falling rate drying period:

$\frac{d\stackrel{\‾}{M}}{\mathrm{d\τ}}=\frac{3\mathrm{\λ}}{{\mathrm{\ρ\γ}}_0\mathrm{\ϵ}{R}_2}[{\stackrel{\‾}{t}}_c-{\stackrel{\‾}{t}}_{\left(\mathrm{\τ}\right)}]---(1-2)$

M is a moisture content in the formula; τ is the time; α is a convection transfer rate; ρ is the latent heat of vaporization, kJ/kg; γ ₀Be the severe of material, kg/m ³R is a material thickness, m; t _(τ)Be the material mean temperature, ℃; t _cBe the medium mean temperature, ℃; λ is the thermal conductivity factor of material, kJ/ (mh ℃); ε is a phase change coefficient;

Learn by following formula, at constant rate drying period, medium temperature t _cWith convection transfer rate α be two principal elements that influence rate of drying, improve medium temperature, increase convection transfer rate (mainly being to increase air flow rate), all help improving rate of drying.And at falling rate drying period, rate of drying just depends on the thermal conductivity factor λ and the phase change coefficient ε of material, and with square being inversely proportional to of the size of material, thereby improve shape and the size that temperature of charge changes material, will be to improve the effective way of rate of drying.Simultaneously, when considering that forced convertion is dry, not only to consider the drying property of l Water Paper base different phase, also will consider the operational characteristic of moulded paper pulp product.In dry run, l Water Paper base surface moisture at first is evaporated, and the difficult evaporation of internal moisture, if the drying medium temperature is too high, l Water Paper base dry tack free gets very fast, cause surperficial knot face sclerosis, and this moment, l Water Paper base inside is still very moistening, and internal moisture is difficult to external diffusion, can reduce rate of drying to a great extent.If it is improper that the temperature curve of technological parameter is provided with, can cause l Water Paper base introversion and extroversion external diffusion gaps between their growth rates to widen, volume contraction appears easily, distortion, phenomenons such as cracking.Therefore, the utility model will design a cover efficiency optimization automatic control system on original hot air convection belt drying line, it will be according to the size and the weight of the drying property and the DIFFERENT WET ground paper of paper mould, adopt ac variable speed technology and modern detecting, temperature according to the scene detection, moisture signal, to circulating fan, MOD, the dehumidifier blower fan, carrier chain driving motor variable-frequency stepless speed-regulating is controlled, and reasonably adjusts the speed of service of conveyer belt in the drying tunnel, operating temperature in each stage drying device, the dischargings of hot blast air quantity and steam etc. form rational drying curve, so that the distortion of product is as far as possible little, saves energy and heat energy loss are accelerated oven dry speed to greatest extent, strengthen the output of drying production line.

This drying line continue to adopt the central heating mode, and central heating systems is made up of combustor (raw material: diesel oil or natural gas) and Combustion of Hot Air Furnace chamber (rolled form by high-quality heat resisting steel); Baking oven adopts frame structure, baking oven length and width determine according to output, baking oven is divided into several dry sections, each drying section is installed a circulating fan and a typhoon machine tailored version frequency converter, the circulating fan air inlet is connected with warm-air pipe and oven interior, and adorns a MOD, and warm-air pipe is connected with the combustion chamber, the circulating fan air outlet is connected with exhaust duct, and exhaust duct is directly sent hot blast on the conveyer belt to.Simultaneously adorn a dehumidifier blower fan in baking oven, in time the steam in the drying line is drained, the drying line profile as shown in Figure 1.

Simultaneously PT100 RTD (temperature sensor) is installed at the every section drying tunnel and the warm-air pipe of drying line, gather the hot blast temperature of warm-air pipe and every section oven dry subregion in real time, at the air inlet of dehumidifier blower fan high temperature resistant humidity sensor is installed and the PT100 RTD is installed, gather the gas temperature of interior steam vapour amount of drying tunnel and discharge drying line in real time at air outlet.Every circulating fan (centrifugal fan 5.5kw, 2900r/min, 6924m ³/ h) by a typhoon machine tailored version Frequency Converter Control, dehumidifier blower fan (centrifugal fan 3kw, 2900r/min, 1481m ³/ h) by a typhoon machine tailored version Frequency Converter Control, frequency converter is realized the control of compressor flow by the frequency of supply of the motor of change blower fan.At the air inlet of circulating fan one MOD (adjusting of changes in temperature wind ratio) is installed, by economical universal frequency converter control MOD (1.1kw) stepless speed regulation operation, thereby automatic damper aperture, the ratio of control hot blast (hot-air of the warm-air pipe) amount of feeding and cold wind (hot-air in the segmentation baking oven) amount of feeding, thus working media (hot-air) temperature in the segmentation baking oven regulated.The carrier chain driving motor adopts universal Frequency Converter Control, and external worm type of reduction gearing, realizes conveyor chain stepless speed regulation control, and drying process as shown in Figure 2.With the control module that adopts PLC as drying line, and expand 12 tunnel A/D modular converter, the PT100 platinum resistance temperature sensor of every section baking oven, the temperature sensor of total warm-air pipe and the humidity sensor in the baking oven all are connected on the A/D module.The external touch-screen of PLC, and handled easily personnel input system technological parameter (as the oven technology temperature, technology humidity, the conveyor chain speed of service, the scale parameter of PID, integral parameter, differential parameter etc.) and the performance parameter of l Water Paper base (as moisture content, size, specific area etc.).PLC realizes communicating by letter with the no-protocol of every frequency converter by the RS484 physical interface.Its control flow such as Fig. 3, shown in Figure 4.

For realizing above-mentioned utility model, the utility model has been analyzed the dry Mathematical Modeling constant rate drying period speed v of drying line ₁

$v_1=\frac{\mathrm{\ρH}(x_0-\stackrel{\‾}{x})}{t_1}---(1-3)$

In the formula, v ₁Be the rate of drying of constant rate drying period, kg/ (m ²H); ρ is the material apparent density that is dried, kg/m ³t ₁Be constant rate drying period time, h; H is a bed depth, m

Constant rate drying period time t ₁

$t_1=\frac{(x_0-x_{\mathrm{cr}}){\mathrm{\ρ\γ}}_w}{3.6K_V(T_1-T_W)}---(1-4)$

In the formula, x ₀Be material moisture content, kg/kg; x _CrBe material critical moisture content, kg/kg; γ _wThe latent heat of vaporization of water during for wet-bulb temperature, kJ/kg; K _VBe the volume overall heat-transfer coefficient, W/ (m ³K); T ₁Be bed of material top hot air temperature, ℃; T _wBe air ' s wet bulb temperature, ℃.

Wherein, volume overall heat-transfer coefficient

K _V＝ρaK _a (1-5)

In the formula, a is a material specific surface area, m ²/ kg; K _aBe overall heat-transfer coefficient, W/ (m ²K).

Overall heat-transfer coefficient K _aCan try to achieve by following formula

K _a＝1.175(G) ^0.37

(1-6)

In the formula, G is the mass velocity of air, kg/ (m ²H).

Wushu (1-6) substitution formula (1-5),

K _V＝ρa1.175(G) ^0.37 (1-7)

Wushu (1-7) substitution (1-4)

$t_1=\frac{(x_0-x_{\mathrm{cr}}){\mathrm{\γ}}_w}{4.23a{\left(G\right)}^{0.37}(T_1-T_W)}---(1-8)$

Constant rate drying period conveyer belt length L ₁

$L_1=\frac{t_1{m}_s}{\mathrm{\ωH\ρ}}---(1-9)$

In the formula, L ₁Be constant rate drying period conveyer belt length, m; m _sBe the material inventory that is dried, kg/h; ω is the conveyer belt effective width, m.Other symbolic significances are the same.

Wushu (1-8) substitution formula (1-9)

$L_1=\frac{(x_0-x_{\mathrm{cr}}){\mathrm{\γ}}_w{m}_s}{4.23\mathrm{a\ωH\ρ}{G}^{0.37}(T_1-T_W)}---(1-10)$

Falling rate drying period time t ₂

$t_2=\frac{\mathrm{\ρH}(x_{\mathrm{cr}}-x_{\mathrm{eq}})}{v_1}\ln \frac{(x_{\mathrm{cr}}-x_{\mathrm{eq}})}{(x-x_{\mathrm{eq}})}---(1-11)$

In the formula, t ₂Be falling rate drying period drying time, h; v ₁Be the rate of drying of constant rate drying period, kg/ (m ²H); X is a l Water Paper base moisture content, kg/kg; x _CrBe l Water Paper base critical moisture content, kg/kg; x _EqBe the final moisture content of l Water Paper base, kg/kg; Wushu (1-3) and (1-8) substitution formula (1-11)

$t_2=\frac{{\mathrm{\γ}}_w(x_0-x_{\mathrm{cr}})(x_{\mathrm{cr}}-x_{\mathrm{eq}})}{4.23a{G}^{0.37}(x_0-\stackrel{\‾}{x})(T_1-T_W)}\ln \frac{(x_{\mathrm{cr}}-x_{\mathrm{eq}})}{(x-x_{\mathrm{eq}})}---(1-12)$

Falling rate drying period conveyer belt length L ₂

$L_2=\frac{t_2{m}_s}{\mathrm{\ωH\ρ}}---(1-13)$

Wushu (1-12) substitution formula (1-13)

$t_2=\frac{{\mathrm{\γ}}_w{m}_s(x_0-x_{\mathrm{cr}})(x_{\mathrm{cr}}-x_{\mathrm{eq}})}{4.23a{\mathrm{\ωH\ρG}}^{0.37}(x_0-\stackrel{\‾}{x})(T_1-T_W)}\ln \frac{(x_{\mathrm{cr}}-x_{\mathrm{eq}})}{(x-x_{\mathrm{eq}})}---(1-14)$

Drying line is made the overall heat perseverance calculates,

q ₁-q ₂＝s(q ₃-q ₄) (1-15)

In the formula, q ₁For material is brought heat into, kJ/h; q ₂For material is taken heat out of, kJ/h; q ₃Hot-air is taken heat out of, kJ/h; q ₄For hot-air is brought heat into, kJ/h; S is a heat idle work loss percentage, %.

Wherein

q ₁＝m _s(c _s+4.187x ₁)T ₁ (1-16)

q ₂＝m _s(c _s+4.187x ₂)T ₂ (1-17)

q ₃＝4.187 .24m _g1T ₃+(595+0.46T ₃)y ₂」 (1-18)

q ₄＝4.187 0.24m _g1T ₄+(595+0.46T ₄)y ₁」 (1-19)

In the formula, m _sBe the material inventory that is dried, kg/h; c _sBe the material specific heat at constant pressure, kJ/ (kgK); T ₁For material advances temperature before the drying box, ℃; T ₂For material goes out temperature behind the drying box, ℃; T ₃Be exhaust temperature, ℃; T ₄Be technological temperature in the drying box, ℃; x ₁For material advances moisture content before the drying box, kg/kg; x ₂For material goes out moisture content behind the drying box, kg/kg; m _G1Be circulating fan flow, kg/h; y ₁For advancing before the circulating fan water yield in the hot-air, kg/h; y ₂The water yield in the hot-air in the drying box, kg/h; Ac three-phase asynchronous motor is the power source of blower fan, and its synchronous rotational speed n is

$n=\frac{60f}{p}---(1-20)$

In the formula, n is the synchronous rotational speed of motor, r/min; F is the motor frequency of supply, Hz; P is a number of pole-pairs.

Motor speed n and compressor flow Q have following relation

$\frac{Q_1}{Q_2}=\frac{n_1}{n_2}---(1-21)$

Therefore, the m of formula (1-17) _G1For

$\frac{m_{g1}}{Q_n}=\frac{60f_1}{{\mathrm{pn}}_n}---(1-22)$

$m_{g1}=\frac{60f_1{Q}_n}{{\mathrm{pn}}_n}---(1-23)$

In the formula, Q _nBe circulating fan nominal air delivery, kg/h; n _nBe the rated speed of motor, r/min; f ₁Be circulating fan frequency of supply, Hz.

Conveyor chain motor operating rate n and material in baking oven the pass of transfer rate are

${\mathrm{nN}}_A=\frac{m_s}{\mathrm{\ρ\ωH}}---(1-24)$

In the formula, N _ASpeed reducing ratio for the conveyor chain reduction box.

Wushu (1-20) substitution formula (1-24) gets conveyor chain motor frequency of supply f ₂With material in baking oven the pass of transfer rate be

$\frac{60f_2{N}_A}{p}=\frac{\mathrm{ms}}{\mathrm{\ρ\ωH}}---(1-25)$

In the formula, f ₂Be the frequency of supply of carrier chain motor, Hz.

Suppose that the warm-air pipe temperature is enough high, then

T ₄＝f ₃N _B (1-26)

In the formula, f ₃Be circulating fan frequency of supply, Hz; N _BBe the throttle opening proportionality coefficient.

In like manner, get with reference to formula (1-23),

$m_{g2}=\frac{60f_4{Q}_m}{{\mathrm{pn}}_m}---(1-27)$

In the formula, m _G2Be dehumidifier fan delivery, kg/h; f ₄Be dehumidifier blower fan frequency of supply, Hz; Q _mBe dehumidifier blower fan metered flow, kg/h; n _mBe dehumidifier blower fan rated speed, r/min.

Its drying production process step is as follows:

Step 1) reaches the drying line length and the segmentation baking oven number ratio (the number ratio of constant rate drying period and falling rate drying period segmentation baking oven) that distributes (1-14) calculated according to planned production output with reference to formula (1-10), and reaches working speed and the operating frequency that (1-25) draws the conveyer belt motor according to formula (1-24).

Step 2) single product to be dried is carried out drying experiment, draw optimum running parameter (the drying process temperature that comprises constant rate drying period and falling rate drying period, air quantity, humidity).

Step 3) is input to PLC with the drying process parameter that above-mentioned steps 1 and 2 draws by touch screen human-computer interface, and touch-screen and PLC are by the communication of RS422 no-protocol.

Step 4) starts drying line by touch-screen to be moved automatically, and product to be dried is dropped into drying line, produces beginning.

The manufacturing parameter that the PT100 platinum resistance temperature sensor of step 5) drying section and humidity sensor are gathered drying line in real time, and by the A/D module analog quantity is transformed into digital quantity and passes to PLC.

Step 6) PLC passes to each MOD frequency converter and dehumidifier fan frequency converter to each digital quantity correspondence by the communication of RS-485 no-protocol.

The inner integrated PID of the frequency converter of each drying section MOD of the step 7) module of adjusting is started working, it can compare according to real time temperature and the default technological temperature that PT100 RTD in the baking oven collects, and of the input of their error amount as the PID controller, and error be multiply by proportionality constant, the integration of error multiply by integral constant, the differential of error multiply by derivative constant, and their addition, thereby obtain the output of PID controller, give the MOD frequency converter result then, thereby regulate the frequency of supply or the rotating operation of motor, reach the purpose of control throttle opening, thereby the feeding ratio of control changes in temperature wind realizes the purpose that hot blast temperature is controlled in the segmentation baking oven.Proportionality constant wherein, integration Changshu, derivative constant is determined by test.

Step 8) is step 7 in like manner, the inner integrated PID of the frequency converter of the dehumidifier blower fan module of adjusting is started working, real-time humidity that it can collect according to humidity sensor in the baking oven and default technology humidity ratio are, and of the input of their error amount as the PID controller, and error be multiply by proportionality constant, the integration of error multiply by integral constant, the differential of error multiply by derivative constant, and their addition, thereby obtain the output of PID controller, give the dehumidifier fan frequency converter result then, thereby regulate the frequency of supply of motor, reach the step-less adjustment of the exhausting amount of dehumidifier blower fan, guarantee that humidity is in the technological requirement scope in the baking oven.Proportionality constant wherein, integration Changshu, derivative constant is determined by test.

Step 9) is passed through the frequency converter long-term work in step 2 and 3 operating frequencies of setting according to the circulating fan of formula (1-23) drying section.

Step 10) repeating step 5-9 makes drying line stably be operated in the optimum process curve.

The control flow of step 1-10 such as Fig. 4, shown in Figure 5.

The existing egg pallet drying production line that needs 1.5 tons of daily outputs of design of concrete operations explanation.The weight of finished product egg pallet is about 65g, and appearance and size is 310mm*310mm*50mm.Egg pallet l Water Paper base psychrometric ratio before the drying after forming is 1:3.4, and promptly moisture content is 70% before the oven dry, and weight is 0.221kg, thickness is 3mm, inventory is 221kg/h, is the convenient hot pressing integer operation that realizes after the oven dry, and the moisture content that now requires the l Water Paper base to go out behind the drying line drops to 10%.Promptly the specific area of l Water Paper base is 0.435m before oven dry ²/ kg carries out baking test to single egg pallet, and the optimum operating temperature that gets constant rate drying period is 160 ℃, and air quantity is 5700m ³/ h, the optimum operating temperature of falling rate drying period is 120 ℃, air quantity is 5400m ³/ h, egg pallet l Water Paper base critical moisture content is 0.846.And to establish the conveyer belt effective width be 1.2m, above-mentioned known parameters substitution Mathematical Modeling formula, constant rate drying period conveyer belt length be about 10m, falling rate drying period conveyer belt length is 15m.If the baking zone segment length is 2.2m, promptly constant rate drying period accounts for 4 drying sections, and falling rate drying period accounts for 7 drying sections.Each drying section configuration circulating fan (centrifugal fan 5.5kw, 2900r/min, a 6924m ³/ h) also can to solve constant rate drying period circulating fan operating frequency by above-mentioned parameter be 39.7Hz, the circulating fan operating frequency of falling rate drying period is 37.6Hz.Conveyor chain motor (2.2kw) operating frequency is 45Hz.Therefore, blower fan, the running frequency 39.7Hz of motor, 37.6Hz, 45Hz reaches 120 ℃ of 160 ℃ of constant rate drying period technological temperatures and falling rate drying period technological temperatures, relative humidity 90% (dehumidifier blower fan working relative humidity) in the baking oven, be input to PLC by touch-screen, drying line just can be worked under the optimum process curve of appointment.Prove that through production practices egg pallet l Water Paper base is after drying through drying line, the product distortion is few, and reaches 10% final moisture content of technological requirement substantially.

Claims (7)

1, a kind of paper pulp molding drying line based on variable-frequency control technique comprises combustor, hot-blast stove, baking oven, circulating fan, dehumidifier blower fan, conveyer belt, and combustor connects hot-blast stove; Above-mentioned baking oven adopts frame structure, and conveyer belt is installed in oven interior, and baking oven length and width determine that according to output baking oven is divided into several drying sections; It is characterized in that: each drying section is equipped with circulating fan, each circulating fan connects blower fan tailored version frequency converter, the hot-air of circulating fan in the circulation baking oven, the circulating fan air inlet also is connected with the warm-air pipe of being drawn by hot-blast stove, between the air inlet of warm-air pipe and circulating fan MOD is housed, MOD is connected with frequency converter; The circulating fan air outlet is connected with exhaust duct, and exhaust duct is directly sent to hot blast on the conveyer belt; The dehumidifier blower fan is housed in baking oven, the dehumidifier blower fan connects blower fan tailored version frequency converter, the mounting temperature sensor respectively at the air outlet place of the central authorities of each drying section of drying line and warm-air pipe, air inlet at the dehumidifier blower fan is installed humidity sensor, at the air outlet mounting temperature sensor of dehumidifier blower fan; The control of drying line is finished by programmable logic controller (PLC) PLC, and PLC passes through to receive the data of each sensor, and compares with the optimal value of setting, and draws regulated quantity and sends control instruction to each frequency converter; Conveyer belt is equipped with driving motor, and driving motor connects frequency converter, and worm type of reduction gearing is installed between driving motor and the conveyer belt; The drying line console is equipped with touch-screen.

2, drying line according to claim 1 is characterized in that: the blower fan tailored version frequency converter that above-mentioned circulating fan connects is to be connected with PLC by the FX2N-485-BD module.

3, drying line according to claim 1 is characterized in that: the blower fan tailored version frequency converter that above-mentioned dehumidifier blower fan connects is to be connected with PLC by the FX2N-485-BD module.

4, drying line according to claim 1 is characterized in that: the frequency converter that above-mentioned MOD connects is to be connected with PLC by the FX2N-485-BD module.

5, drying line according to claim 1 is characterized in that: the frequency converter that the said conveyer belt driving motor connects is to be connected with PLC by the FX2N-485-BD module.

6, drying line according to claim 1 is characterized in that: the said temperature sensor is connected with PLC by the FX2N-8AD module with humidity sensor.

7, drying line according to claim 1 is characterized in that: above-mentioned touch-screen is to be connected with PLC by RS-422.

Images