1.INTRODUCTION

1.1Pneumatic conveying system

A pneumatic conveying system is a process by which bulk materials of almost any type are transferred or injected using a gas flow as the conveying medium from one or more sources to one or more destinations. Air is the most commonly used gas, but may not be selected for use with reactive materials and/or where there is a threat of dust explosions.

A well designed pneumatic conveying system is often a more practical and economical method of transporting materials from one point to another than alternative mechanical systems (belt conveyors, screw conveyors, vibrating conveyors, drag conveyors and other methodologies) because of three key reasons:

1. First, pneumatic systems are relatively economical to install and operate

2. Second, pneumatic systems are totally enclosed and if required can operate entirely without moving parts coming into contact with the conveyed material. Being enclosed these are relatively clean, more environmentally acceptable and simple to maintain

3. Third, they are flexible in terms of rerouting and expansion. A pneumatic system can convey a product at any place a pipe line can run.

1.2 Definition of Pneumatic Conveying

Pneumatic conveying is a material transportation process, in which bulk particulate materials are moved over horizontal and vertical distances within a piping system with the help of a compressed air stream. Using either positive or negative pressure of air or other gases, the material to be transported is forced through pipes and finally separated from the carrier gas and deposited at the desired destination. A general setup of a pneumatic conveying system This mode of bulk solid transportation holds an important position in the particulate material handling field, because of a series of advantages over other modes of transportation. It has a wide range of applications, with examples ranging from domestic vacuum cleaners to the transport of some powder materials over several kilometres. With a recorded history of more than a century, pneumatic conveying systems have been popularised in the bulk material handling field.

1.3 History of Pneumatic ConveyingPneumatic tubes used for transporting physical objects have a long history. The basic principles of pneumatics were stated by the Greek Hero of Alexandria before 100 BC On the other hand, the concept of conveying materials in pipeline systems also goes back to pre-historical age with some evidence of that the Romans used lead pipes for water supply and sewage disposal and the Chinese used bamboo to conveynatural gas. Although there had been various applications of pneumatic conveying earlier inmany civilisations, the first documented pipeline conveying of solid particles was recorded in 1847. In Peugeot plant in France, the pneumatic conveying principle was

used for the exhaust of dust from number of grindstones with the help of an exhaust fan.

Pneumatic tubes used for transporting physical objects have a long history. The basic principles of pneumatics were stated by the Greek Hero of Alexandria before 100 BC [2]._On the other hand, the concept of conveying materials in pipeline systems also goes back to pre-historical age with some evidence of that the Romans used lead pipes for water supply and sewage disposal and the Chinese used bamboo to conveynatural gas [3].Although there had been various applications of pneumatic conveying earlier in many civilisations, the first documented pipeline conveying of solid particles was recorded in 1847 [4]. In Peugeot plant in France, the pneumatic conveying principle was used for the exhaust of dust from number of grindstones with the help of an exhaust fan.In 1864, an experimental pneumatic railway was built at Crystal palace with the intention of using the principle of vacuum applied to a railway tunnel to move a carriage, which had been fitted with a sealing diaphragm [5]. Another application of vacuum pneumatic transport was reported in ship unloading plant in London in 1890. A number of applications of operational principles of pneumatic transport couldbe seen in last decade of the 19th century at some places in Europe [4, 6] and especially, in the grain transport and handling field [5]. During this time period, general break through events in the evolution of pneumatic conveying systems such as use of negative pressure systems, invention of auxiliary equipments like rotary feeders, screw feeders, valves, etc., could be emphasised. During early decades of 20th century, it was common practice to use pneumatic conveying to transport grain [6]. Ref. [7] presented a chronology of pneumatic pipeline highlighting the innovatory individuals and companies, especially duringearly and middle era of 20th century. During the First World War, the development of pneumatic conveying was influenced by the high demand for foods, labour scarceness and risks of explosion. Since the pneumatic conveying systems were seen as the answer for those situations, a huge evolution of pneumatic transport was achieved during that time period. In the post-war period, pneumatic conveying systems were used for more industrial related materials like coal and cement.Beginning of theoretical approaches, invention of blowers, introduction of batch conveying blow tanks, etc., were among the highlighted milestones of the evolution of pneumatic transport systems during this era.Nowadays, pneumatic transport is a popular technique in particulate material handling field. It has been reported that some plants have transport distance of more than 40 km [8], material flow rate of few hundreds tons per hour and solid loading ratio (the mass flow rate ratio between solid and air ) of more than 500.

1.4 classification of pneumatic conveying systemsPneumatic transport systems can be classified in a number of ways. Among them, the Nature of system pressure and the mode of conveying are the two major aspects for The classification. So far as the system pressure is concerned, there are three major Types of transport systems, which can briefly be explained in the following way:- 1. Positive pressure systems In this type of pneumatic conveying system, the absolute pressure of conveying gas inside the piping system is always greater than atmospheric pressure. This configuration is seen as the most famous type of pneumatic conveying system, especially in multiple discharge applications, in whichthe conveying material is picked up from a single point and delivered to several receiving stations.2. Negative pressure systems This type is also termed as vacuum/suction conveying where the absolute gas pressure inside the system is lower than atmospheric pressure. The simplest example for negative pressure pneumatic conveying may be the domestic vacuum cleaner and it varies from this application to heavy duty ship unloader. Especially in transport of toxic and hazardous materials, a negative pressure system may be the best choice since it allows dust free feeding and provides leak free material handling. This configuration is generally used for the transport of material from several feeding points to a common collection station.3. Combined negative-positive pressure systems –To overcome the weaknesses and combine the advantages of positive and negative pressure systems, some plants can be seen in operation combining both these configurations together. This type is also termed as ‘suck-blow’ system where multiple feeding as well as multiple deliveries are easy to perform. As mentioned earlier in this section, the other classification method of pneumatic conveying systems is based on the modes of transportation, which depends on air velocity and at the pipeline inlet. According to this aspect, pneumatic conveying systems can be classified into two different categories, which can be brieflydescribed as below;1. Dilute phase conveying systems -By employing large volumes of gas at high velocities, particulate material transportation in suspension mode is usually termed dilute phase conveying. In this mode, the bulk material is carried by an air stream of sufficient velocity to entrain and re-entrain it for a distance, which depends on the available pressure .2. Dense phase conveying systems –By reducing the gas velocity, bulk materials can be transported in stratification mode with non-uniform concentration of solids over the pipe cross-section. The material is pushed through a pipeline as a plug, which occupies the whole cross section or as a moving bed for a pressure dependent distance [12]. Even though there are different terms to define the different conveying patterns under reduced gas velocity, such as plug flow, slug flow, strand flow, moving beds, etc, in general, they all come underdense phase conveying. The definition of the above two modes of transportation is controversial with the different views of different researchers regarding the setting up of boundary in

between them. Some researchers use solid mass loading ratio, which is the ratio between the solid mass flow rate and the gas mass flow rate, to demarcate the boundary, while others use conveying air velocity. Even with those concepts, many discrepancies have been reported in literature in case of the definition of transport mode

1.5 Principle of pneumating conveying systemPneumatic conveying is achieved by creating a pressure differential along a pipeline and using the air that moves toward the area of lower pressure to move bulk material.

1.6 Working of pneumatic conveying systemFollowing step involves in working of Pneumatic Conveying System

1. Air is compressed in a air compressor and stored in a Air Receiver Tank.2. Powder materials stored in a storage tank .3. Then Air is go through pipe line to Transporter where air is mixed with powder materials 4. Air inlet to Transporter via a Vent Valve.5. Then these mixture carried out where it is used .

1.7 Operation of a Pneumatic Conveying SystemVarious flow regimes exist inside the pipeline in a pneumatic conveying system, straddling the entire range of conveying conditions from extrusion flow (packed bed) to fully dilute suspension flow. Through numerous experimental studies together with visual observations using glass tubes, etc, scientists have concluded these varieties of flow regimes. It has been seen that these different flow regimes could beexplained easily in terms of variations of gas velocity, solids mass flow rate and system pressure drop. This clarification also explains the general operation of a pneumatic conveying system.Most of the research workers and industrial system designers have used a special graphical technique to explain the basic operation of a pneumatic conveying system. This technique utilises the interaction of gas-solid experienced inside the conveying pipeline in terms of gas velocity, solids mass flow rate and pressure gradient in pipe sections in a way of graphical presentation, which was initially introduced by Zenz. Some researchers named this diagram as pneumatic conveying characteristics curves, while others used the name of state or phase diagram. The superficial air velocity and pressure gradient of the concerned pipe section are usually selected as the x and y axes of the diagram and number of different curves are produced on these set of axes in terms of different mass flow rates of solids. There is a distinguishable difference between the relevant flow regimes for horizontal and vertical pipe sections. On the other hand, the particle size and particle size distribution also have influence on the flow patterns inside the pipelines. The general operation of horizontal and vertical pneumatic conveying systems are briefly explained in the following sections with the help of pneumatic conveying phase diagrams together with varieties of flow regimes.1.7.1 Horizontal ConveyingOne typical horizontal phase together with variouscross-sectional diagrams showing the state of possible flow patterns at different flowsituations. The variations of constant solids mass flow rate contours, when the conveying gas velocity and system pressure drop variesindependently. The gas only line shows the pressure drop vs. gas velocity curve,which is characteristically a single phase flow. When the solids particles are

introduced to the system with a particular solids mass flow value, the pressure dropincreases to a higher value than in case of gas only transport even though the gasvelocity is maintained constant. By keeping the solids flow rate constant and reducing the gas velocity further, pressure drop decreases down to a certain point where the minimum pressure drop is experienced. The pressure minimum curv connects such points for different solids flow rate values. Generally, the flo regimes up to this point from the right hand could be categorized as the dilute phase flow with low values of mass loading ratios. Further reduction of gas velocity lead to particle deposition in pipe bottom and then the flow mode is called dense phase conveying. Pressure drop can be seen increasing, when gas velocity is decreasing.After an unstable flow region, the conveying pattern shows a plug flowcharacteristic, which will cause the pipeline to be totally blocked in attempts of further reduction of gas velocity. One boundary is the extreme right hand side limitation, which depends on the air volume flow capacity of the prime mover. The upper limit of the solid flow rate is influenced by the allowable pressure value of compressed air supply. The left-hand side boundary is fixed by the minimum conveying velocity, which will be discussed in details in later chapter.1.7.2 Vertical ConveyingThe orientation of the pipe makes a considerable effect to the flow patterns and conveying regimes, because of the influence of gravity force. Consequently, the cross-sectional diagrams are totally different for the vertical pipe sections from those of horizontal sections, although the general appearance of the mass flow rate contours are similar to each other. Figure 1-9 shows a typical phase diagram of a vertical pipe section, together with various cross-sectional diagrams showing the representative state of possible flow patterns at different flow situations.

2. Aim of the ProjectThe investigation was planned to address the whole conveying system, i.e., from the feeding point to the receiving tank, including all typical components on it. Consequently, the final aim of the current investigation was to formulate a reliable design technique, which can be used in the design and scaling up of pneumatic conveying system.This can be accomblish by desining a venturi system which create a suction effect through which we can transfer the material from one place to another place without any air leakage.2.1 Applications of Pneumatic ConveyingThe applications of pneumatic conveying systems can be seen in many industrialsectors. A list of industrial fields where it has extensively been used is given below;Chemical process industryPharmaceutical industryMining industryAgricultural industryMineral industryFood processing industry

2.2 Limitations

A relatively high air volume and velocity is required: so power requirements are also high. Higher air velocities will have the following other disadvantages:

1. The wear caused by the product on the pipe is considerably higher therefore this process is NOT suitable for materials which are susceptible to degradation and/or are abrasive in nature.

2. The products can get deformed or crushed therefore this process is NOT recommended for friable products

3 BACKGROUND AND REVIEW OF LITERATURE3.1 IntroductionAs explained in Chapter 1, this experimental investigation addresses the whole conveying line by considering the individual components separately in order to formulate a detailed scaling up technique for the dilute and dense phase pneumatic conveying systems. In order to gain an understanding of the flow phenomenon I different sections of pneumatic conveying system and how different researches addressed these issues, a detailed literature survey was done on the available model and descriptions of the gas-solids flow in closed pipelines in laboratory scale and much longer pneumatic transport lines of industrial scale as well. To understand thecurrent situation of the available theoretical descriptions, in the sense of how far theyare tallying or contradicting each other was another objective of this literature review.In this literature review, gas-solid flow in pipes is described with help of some suggested mechanisms that have been proposed in open literature. Simultaneously, the models available to explain the large scale pneumatic rigs were used to compare them with each other. To cover those models, in the first part of this section, the conveying line is virtually divided into different sections, such as;a) feeding devices and entry sectionb) horizontal pipesc) pipe bendsd) vertical sections, etc, where distinguishably different flow behaviour could be expected and the available theoretical descriptions relevant to these sections are discussed. It starts from the beginning of the conveying line and proceeds along the pipeline upto the end of transport line, by considering different sections and components. After that, the models, which explain the whole conveying line as aglobal one, are reviewed. Finally, the available scale-up procedures based on mathematical descriptions are also discussed in details.In addition to the mathematical and stochastic models, numerical computational methods have also been extensively used to describe the flow phenomenon of gassolids flow during the last decade. Under this literature survey, computational fluid dynamics models were also discussed.3.2 Entry sectionIn the entry section, the flow behaviour and the pressure losses incurred basically depend on the feeding device. Usually, the feeding systems are classified on the basis of pressure limitations, since their function of the physical constructions are couple with methods of sealing. In terms of commercially available feeding devices, it is convenient to classify feeders in three pressure ranges.In the case of the first two devices, they are capable of feeding at a controlled rate and continuous operation and, they are especially suitable for low-pressure (up to 1.0 bar) systems, operating with fans or blowers [30]. The incorporation of a rotary valve at the bottom of a feeding tank is perhaps the more common technique of effectin solids flow control. It is common practice to fit a variable speed drive to the valve,thereby affecting the control. Where it is required to convey a product over long distances and/or in dense-phase, a high pressure system is used and feeding into

high-pressure systems almost always involves the use of blow tanks, which usually are capable of working pressures upto 7 ~ 10 bars.3.3 Blow TankBlow tanks are very often used in pneumatic conveying systems, as they offer a wide range of conveying conditions, both in terms of pressure and flow rates. Basically, there are two modes, which are called discontinuous mode and continuous mode.These modes can respectively be achieved using single and twin blow tank systems . A single blow tank system is only capable of conveying single batches. In order to ensure continuous flow, it is accepted practice to use two blow tanks fitted to a common discharge line. The simplest type of dense phase pneumatic conveying feeder, a high pressure blow tank with a fluidising membrane at the bottom, issuccessfully being used for wide varieties of particulate materials.3.3.1 Top Discharge and Bottom DischargeBlow tanks are typically available in two different structures; ‘Fluxo type’ – top discharge and ‘Cera type’ – bottom discharge, which generally refers only to th direction, in which the contents of the vessel are discharged. In top discharge blow tanks, normally porous membrane is used to fluidise the material. For a give product, top- and bottom-discharge blow tanks will differ in their performance. Mills studied this phenomena and recommended the top-discharge tanks for products to be conveyed in dense phase, as they provide better control for this mode of conveying. The top-discharge tanks seemed to achieve the highest feed rates, according to his findings. On the other hand, in the top discharge blow tank system with fluidising membranes, the pressure drop across the membrane and the discharge pipe is comparatively high. If the fluidising air flow rate is high and/or the membrane area is small, the pressure drop further increases. However, he recommended bottomdischarge tanks for granular materials. In fact, top-discharge type may not be able to handle them at all, because the ease of air permeation through the mass of granulesmay prevent the build-up of enough lift. Marcus et al. found that the discharge performance from a blow tank can be significantly influenced by the method of introducing air into the blow tank. With some products, by adding air to the top of the material, the highest rate was obtained. Other materials performed better when the air was introduced into the material via a nozzle located at the discharge pipe.Jones et al.compared the performance differences between top and bottom discharge blow tanks and found that there is no significant difference in the pressure,and thus the energy, required to convey a product through a pipeline at a given mass flow rate and loading condition in both configurations.3.3.2 Velocity at Entry SectionAnother important parameter at the entry section is the start gas velocity, which is also termed as pickup velocity, saltation velocity and critical velocity in some literatures. Due to the continuous expansion of the conveying gas over the conveying distance, the gas velocity at the start of the pipeline is the lowest gas velocity in the conveying system having a constant bore size. Nowadays, some industrial pneumatic conveying systems are using stepped pipelines to avoid the continuous increase of conveying velocity alone the conveying line. In those cases, there may be a possibility to have low conveying velocities at the pipe sections where the diameter

enlargements are available. To avoid pipeline blockages and to facilitate an efficient conveying without high particle degradation, an optimum value of the start gas velocity should be chosen at the entry section of the conveying line. The determination of minimum conveying velocity has been a topic for a vast number of researches 3.4 Horizontal Pipe SectionsUsually, horizontal sections are the most common pipe sections in industrial pneumatic conveying installations. The flow pattern existing in two-phase, gas-solid mixtures travelling along horizontal pipes have been studied by many researches using theoretical aspects and visual observations. According to their findings, these patterns are principally dependent upon the velocity of the gaseous phase, the ratio of the mass flow rate of solids to the mass flow rate of gas (i.e., the ‘solids loading ratio/ phase density’) and the nature of particulate solid material being conveyed. These flow patterns have been discussed with several aspects, specially, in terms of modes of transportation, i.e., dilute and dense phase conveying. However, there is no uniformity in terminology, which adds the confusion of understanding thephenomena. Although it is difficult to define the boundaries between the dense phase and dilute phase flow modes, the conveying air velocity and the solids loading ratio have been used more frequently to categorise these flows. Many dilute-phas conveying systems are known to operate with solid loading ratio less than 15,whereas for dense phase that is greater than 15. In some research papers the flow is considered as dilute phase upto solids loading ratio of 30. In terms of air velocity, to have the dilute phase conveying it is necessary to maintain a minimum value of conveying air velocity is generally of the order of 13 to 15 m/s [16]. The flow is considered as medium phase when solids loading ratio is above 30, where the conveyance occurs with moving beds and dunes accompanied by more or les segregation. The flows with loading ratios of much larger values than 30 and with approximate inlet air velocity of 7 m/s, conveyance occurs as plugs with high pressure gradients but low velocities, which is called as dense phase transport.3.5. Dense Phase TransportAs discussed early in Chapter 1, the use of the term ‘Dense Phase’ is far from being precise. Some have used the word in pneumatic conveying to mean solid particles flowing at a velocity less than their saltation velocity. Some researchers have used the phase diagram to designate the region to the left of the minimum pressure dro curves as the dense phase region of flow. In spite of these discrepancies in definitions of the dense phase conveying, it has been the main subject of considerable number of theoretical and experimental research works over a substantial period of time.Because of the number of advantages over dilute phase transport, this has bee acquiring more industrial applications during the past period of time. In particular, the low rates of pipe wear and particle attrition that are obtained with the low velocities involved and less air requirement thus the low power consumption areamong the advantages of dense phase conveying. But, unfortunately, there are number of uncertainties, design difficulties and unforeseen pipe blockages, most of which arise from the fact that the precise mechanism by which the particles are conveyed has never been well understood. Among the vast number of literatures on

dense phase conveying, few of them, which show a comparatively good agreement with the experimental data and are well documented, has been selected for this study. In this section, the models o horizontal dense phase conveying are considered and the vertical sections and the velocity concepts will be discussed in their respective sections The work done by Konrad et al. could be seen as one of the earliest and frequently cited publication by fellow reseachers. They developed a theoretical model to predict the pipeline pressure drop in horizontal dense phase plug conveying. They describe the flow mechanism with following phenomenal concepts.The material is conveyed only in the plugs and in the regions just in front and behind them.There is a layer of stationary material between the plugs.The flow pattern is similar to that of a gas-liquid system.

4. MODE OF CONVEYINGMuch confusion exists over how materials are conveyed through a pipeline and to the terminology given to the mode of flow. First it must be recognized that materials can either be conveyed in batches through a pipeline, or they can be conveyed on a continuous basis, 24 h a day if necessary. In batch conveying the material may be conveyed as a single plug if the batch size is relatively small. For continuous conveying, and batch conveying if the batch size is large, two modes of conveying are recognized. If the material is conveyed in suspension in the air through the pipeline it is referred to as dilute phase conveying. If the material is conveyed at low velocity in a non-suspension mode, through all or part of the pipeline, itis referred to as dense phase conveying.4.1 Dilute phaseAlmost any material can be conveyed in dilute phase, suspension flow through a pipeline, regardless of the particle size, shape or density. It is often referred to as suspension flow because the particles are held in suspension in the air as they are blown or sucked through the pipeline. A relatively high velocity is required and so power requirements can also be high but there is virtually no limit to the range of materials that can be conveyed.There will be contact between the conveyed material and the pipeline, and particularly the bends, and so due consideration must be given to the conveying of both friable and abrasive materials. With very small particles there will be few impacts but with large particles gravitational force plays a part and they will tend to ‘skip’ along horizontalpipelines.Many materials are naturally capable of being conveyed in dense phase flow at low velocity. These materials can also be conveyed in dilute phase if required. If a high velocity is used to convey any material such that it is conveyed in suspension in the air, then it is conveyed in dilute phase.4.2 Dense phaseIn dense phase conveying two modes of flow are recognized. One is moving bed flow, inwhich the material is conveyed in dunes on the bottom of the pipeline, or as a pulsatile moving bed, when viewed through a sight glass in a horizontal pipeline. The other mode is slug or plug type flow, in which the material is conveyed as the full bore plugs separated by air gaps. Dense phase conveying is often referred to as non-suspension flow. Moving bed flow is only possible in a conventional conveying system if the material to be conveyed has good air retention characteristics. This type of flow is typically limited to very fine powdered materials having a mean particle size in the range of approximately 40–70_m, depending upon particle size distribution and particle shape. Plug type flow is only possible in a conventional conveying system if the material has good permeability. This type of flow is typically limited to materials that are essentially mono-

sized, since these allow the air to pass readily through the interstices between the particles. Pelletized materials and seeds are ideal materials for this type of flow.4.3Conveying air velocityFor dilute phase conveying a relatively high conveying air velocity must be maintained .This is typically in the region of 12 m/s for a fine powder, to 16 m/s for a fine granular material, and beyond for larger particles and higher density materials. For dense phase conveying, air velocities can be down to 3 m/s, and lower in certain circumstances. This applies to both moving bed and plug type dense phase flows. These values of air velocity are all conveying line inlet air velocity values. Air is compressible and so as the material is conveyed along the length of a pipeline the pressure will decrease and the volumetric flow rate will increase.

4.4 Particle velocityIn dilute phase conveying, with particles in suspension in the air, the mechanism of conveyingis one of drag force. The velocity of the particles, therefore, will be lower than that of the conveying air. It is a difficult and complex process to measure particle velocity, and apart from research purposes, particle velocity is rarely measured. Once again it is generally only the velocity of the air that is ever referred to in pneumatic conveying. In a horizontal pipeline the velocity of the particles will typically be about 80% of that of the air. This is usually expressed in terms of a slip ratio, defined in terms of the p1V1= p2V2

5. MATERIAL VELOCITY

In dilute phase conveying, with particles in suspension in the air, the mechanism of conveying is one of drag force. The velocity of the particles, therefore, will be lower than that of the conveying air. It is a difficult and complex process to measure material velocity, and apart from research purposes, particle velocity is rarely measured. It is generally only the velocity of the air that is ever referred to in pneumatic conveying.

1. In a horizontal pipeline the velocity of the particles will typically be about 80% of that of the air. This is usually expressed in terms of a slip ratio, defined in terms of the velocity of the particles divided by the velocity of the air transporting the particles, and in this case it would be 0.8.

2. In vertically upward flow in a pipeline a typical value of the slip ratio will be about 0.7.

These values relate to steady flow conditions in pipelines remote from the point at which the material is fed into the pipeline, bends in the pipeline and other possible flow disturbances. At the point at which the material is fed into the pipeline, the material will

5.1 Solids loading ratioSolids loading ratio, or phase density, is a useful parameter in helping to visualize the flow. It is the ratio of the mass flow rate of the material conveyed divided by the mass flow rate of the air used to convey the material. It is expressed in a dimensionless for where is the solids loading ratio (dimensionless), m˙ p, the mass flow rate of material (kg/min) and m˙ a, the mass flow rate of air (kg/min).Since the mass flow rate of the conveyed material, or particles, is usually expressed in tonne/h and the mass flow rate of the air is generally derived by calculation in kg/s. A particularly useful feature of this parameter is that its value remains essentially constant along the length of a pipeline, unlike conveying air velocity and volumetric flow rate, which are constantly changing.

For dilute phase conveying, maximum values of solids loading ratio that can be achieved are typically of the order of about 15. This value can be a little higher if the conveying distance is short, if the conveying line pressure drop is high, or if a low value of conveying air velocity can be employed. If the air pressure is low or if the pipeline is very long, then the value of solids loading ratio will be very much lower.For moving bed flows, solids loading ratios need to be a minimum of about 20 before conveying at a velocity lower than that required for dilute phase can be achieved.Solids loading ratios, however, of well over 100 are quite common.The data presented in this Design Guide on materials such as cement and fine fly ash, solids loading ratios in excess of 100 are reported, whether for horizontal or vertical flow.In conveying barytes vertically up the author has achieved a solids loading ratio of about 800 with a short pipeline. Conveying at very low velocity is necessary in order to achieve very high values of solids loading ratio in moving bed flow. This is because air flow rate is directly proportional to air velocity and air flow rate is on the bottom line.For plug type flow the use of solids loading ratio is not as appropriate, for the numbers do not have the same significance. Since the materials have to be very permeable, air permeates readily through the plugs. Maximum values of solids loading ratio, therefore, are only of the order of about 30, even with high values of conveying line pressure drop. If a material is conveyed at a solids loading ratio of 10, for example, it could be conveyed in dilute phase or dense phase. It would only be with the value of the conveying line inlet air velocity that the mode of flow could be determined.

6. RECENT DEVELOPMENTSAlthough pneumatic conveying systems have numerous advantages over alternative mechanical conveying systems for the transport of materials, they do have drawbacks, particularly for materials that can only be conveyed in dilute phase. Particle degradation and erosive wear of pipeline bends are particular examples. Due to the high conveyin air velocity required, energy requirements are also high.In recent years there have been many developments of pneumatic conveying systems aimed at increasing their capability for conveying a wider range of materials in dense phase, and hence at low velocity. This has generally been achieved by conditioning the material at the feed point into the pipeline, or by providing a parallel line along the length of the pipeline to artificially create either permeability or air retentionin the material. 6.1 System typesPneumatic conveying system types can be divided into conventional and innovatory types. In conventional systems the material to be conveyed is simply fed into the pipeline and it is blown or sucked to the discharge point. It must be realized that low velocity dense phase, conveying in conventional pneumatic conveying systems is strictly limited to materials that have the necessary bulk properties of good air retention orgood permeability. The use of high pressure air is not synonymous with dense phase conveying. It is dictated entirely by the properties of the material to be conveyed in a conventional conveying system.Probably the majority of materials that are conveyed have neither of these properties.There has, therefore, been much research undertaken into pneumatic conveying with a view to developing systems that are capable of conveying a much wider range of materials in dense phase and hence at low velocity. Making these systems mor suitable for abrasive and friable materials has provided a particular driving force.6.2 System designThis group of chapters is concerned with the design of pneumatic conveying systems.The first two chapters are devoted to the considerations of air alone, but it is here that the basic modelling for pneumatic conveying begins. Materials are then added to the pipeline and the influence of the materials is considered and compared.

6.2.1 Air flow rate evaluationAir is compressible with respect to both pressure and temperature, and air movers are generally specified in terms of ‘free air conditions’. The correct specification of an air mover in terms of volumetric flow rate is essential in terms of achieving the correct conveying air velocity. The derivation of all the models necessary is given and the results are displayed graphically. The equations are presented in terms of both volumetric flow rate and conveying air velocity, so that they can be used for the design of future systems, as well as the checking of existing systems. 6.2.2 Air only relationshipsThe reference point for any pneumatic conveying system is the performance of the empty pipeline, and so equations are developed that will allow the air only pressure drop to be evaluated for any pipeline system. Bends and other pipeline features are considered for both positive pressure and vacuum conveying systems. Models and methods for air flow rate control are also included.6.2.3 Conveying characteristicsConveying characteristics for a material provide a valuable aid to system design. They provide the design data in terms of air flow rate and air supply pressure for a given material flow rate and quantify the effect of pipeline bore and conveying distance. In addition the conveying characteristics identify the minimum conveying conditions and provide the means to determine power requirements, thus enabling comparisonsto be made for different conveying systems. Conveying characteristics are presented for representative materials and, in addition to total pipelines, data is also presented for individual sections of pipeline, as well as bends.

6.2.4 Conveying capabilityIn this chapter the conveying characteristics of a much wider range of materials are presented to illustrate the full influence that different materials can have on conveying capability and performance. High and low pressure and dilute and dense phase conveying are considered for a broad range of materials.

6.2.5 Material property influencesA goal in pneumatic conveying is to make it possible to design a pneumatic conveying system without the need for carrying out full-scale conveying tests with a material.The results of a study into correlations between material properties obtained from bench scale tests and material conveying characteristics obtained from full-scale pneumatic conveying trials are given. Correlations were sought as to whether a material will convey in dense phase and what type of pressure drop/material flow rate characteristic is to be expected. The work is extended by investigating the influence that conveying itself might have on the subsequent conveying performance of a material.

6.2.6 Pipeline scaling parametersIt is generally not practical to replicate a plant pipeline for the purposes of undertaking tests in order to design a conveying system. Over the years, however, with the accumulation of practical experience and specific research programmes, scaling parameters have been developed for the purpose. These will take account of the differences between a test facility pipeline and a plant pipeline with respect to lengths of horizontal and vertical pipeline, number and geometry of bends, and pipeline bore. In addition to these parameters, pipeline material and pipeline steps are also considered.

6.2.7 Design procedures

Logic diagrams are presented for pneumatic conveying system design based on both mathematical models and test data. They are presented for the purpose of checking the capability of an existing system, as well as for the design of a new system. Some of the available equations and bench scale test correlations are evaluated and the more useful relationships are included to show how they can be used in conjunction with the logic diagrams..6.2.8 First approximation design methodsVery often a first approximation solution is all that is required. This may be for system design purposes, particularly if a feasibility study is being carried out, or to provide a quick check on the performance of an existing system. An approximate value of power required is often required so that the operating cost of such a system can be estimated in terms of pence per kg.Two such methods are included, one of which can be used for dense phase conveying systems in addition to dilute phase.

6.2.9 Multiple use systemsIn many industries more than one material is required to be conveyed by the same system. Different materials, however, can have very different conveying characteristics. Some have very different air requirements as well as different flow rate capabilities. There are also many systems that require material to be conveyed over a range of distances.Conveying distance, however, has a marked effect on material flow rate and can influence air flow rate in certain situations. These various conveying situations are considered and a variety of solutions are presented.

7. SYSTEM OPERATIONThis group of chapters is concerned with the operation of pneumatic conveying systems. Pipeline blockages, do unfortunately occur, but mainly due to poor design and maintenance and so this topic is given particular consideration. Means of improving the performance of an existing system are considered, which may be to reduce power requirements or to increase material flow rate. Many problems relate to the propertiesof the conveyed material, and not least of these are abrasive and friable materials an so one chapter is devoted to erosive wear and another to particle degradation. Moisture and condensation is similarly considered, as well as the issues relating to health and safety. Due to the complexities of system design, a lack of reliable design data, and a poor understanding of compressible flow, many pneumatic conveying systems pose numerous problems on commissioning. Pipeline blockage and conveying systems not capableof achieving the desired material flow rate are common problems. A detailed analysis of all possible causes is given and a checklist is provided for quick reference.

7.1 Optimizing and up-rating of existing systemsIn some cases, if a system is over designed, it may be possible to optimize the conveying parameters and either reduce the power requirement for the system or increase the conveying capability. Very often an increase in conveying performance is required for an existing system and so the procedures for reviewing the possibility are explained in detail. The procedures are given for both positive pressure and vacuum conveying systems.

7.2 Operating problems

Potential users are often reluctant to install a pneumatic conveying system because they anticipate operating problems. Pneumatic conveyors can experience problems but the situation has been improved by the introduction of new types of conveyor and by the modification of existing systems, based on a better understanding of the mechanisms of conveying. This often results in a choice of solutions to a particular problem. The most common problems affecting pneumatic conveyors are examined, such as static electricity and material deposition. Some practical solutions to these problems are presented.

7.2.1 Erosive wearMany materials that have to be conveyed are very abrasive, such as silica sand, alumina, cement and fly ash. As a consequence the conveying pipeline, bends and various components that are exposed to impact by the gas–solids flows have to be specified such that the problem is minimized to an acceptable level. It is not uncommon for steel bends installed in a pipeline conveying an abrasive material to fail in a matter of hours.The mechanics of the erosive wear process is explained, and a review of possible preventative measures that can be taken, and alternative components or materials that can be used, is given.

7.2.2 Particle degradationMany materials that have to be conveyed are friable and so particles are liable to be broken when they impact against retaining surfaces, such as bends in the pipeline. It is for this reason that pneumatic conveying systems are not generally used for this type of material. There are numerous means by which the problem can be reduced, however, relating to conveying conditions, bend geometry and materials of construction and so a detailed review of these is given.7.2.3 Moisture and condensationAs the temperature of air reduces the capacity for air to support moisture reduces and condensation is likely to occur. The same situation occurs with an increase in pressure. Air is the prime mover in pneumatic conveying systems and changes in both temperature and pressure are very common. The modelling of air with respect to moisture is presented to illustrate the nature of the problem and to provide guidance on the potential magnitude of the problem, and for the sizing of air drying plant and equipment should this be required.

7.2.4 Health and safetyMost dusts pose a potential health problem, and many materials that have to be conveyed are potentially toxic. Pneumatic conveying is often chosen for hazardous materials because the system provides a theoretically totally enclosed environment for their transport. It is also considered that the majority of conveyed materials are potentially explosive, and this certainly applies to most food products, fuels, chemicals and metal powders. In this chapter a detailed review of precautions and modifications to plantand components is given. The nature of the problems is explained and information on appropriate measurable properties of dust clouds is provided.

8. Universal conveying characteristics methodThe pressure required to convey a material through a pipeline can be divided into a number of component parts. The most important are the straight pipeline sections and the bends. For each of these elements there are a multitude of sub variables that can have and influence, but their incorporation necessarily adds to the complication of the process. A compromise is clearly needed in order to provide a quick first approximation method.

8.1 Straight pipeline

One of the most easiest method of convey the material from one place to other place is by using the horizontal pipe. This is the simplest method because of less pressure drop.

8.2 Vertical pipelinesFor flows in vertically down sections of pipeline the situation is very different. In dense phase flows there is a pressure recovery, such that the pressure gradient has a negative value. For dilute phase flows, however, there is a pressure loss. The transition between the two occurs at a solids loading ratio of about 35 and at this value materials can be conveyed vertically down with no pressure drop at all. therefore, cannot be used in this case. If, in a long pipeline, there is only a very short length of vertically down pipeline, it is suggested that it can be ignored, in terms of the overall accuracy of this method, for both and dense phase flows. If a conveying system does have a significant proportion of pipeline which is vertically down, the user if referred conveying characteristics.

8.3 Pipeline boreMaterial flow rate varies approximately in proportion to pipe section area, and hence in terms of (diameter). Air flow rate, to maintain the same velocity in a pipeline of different bore, varies in exactly the same way. To determine the pressure gradient for flow in a pipeline having a bore different from that of the reference data . both the material and air flow rates should be adjusted in proportion to (d2/53)2, where d2 is the diameter of the plant pipeline in mm. It will be noted that there will, therefore, be no change in the value of the solids loading ratio.

8.4 Stepped pipelinesWhen high pressure air is employed it is usual to increase the bore of the pipeline to a larger diameter along the length of the pipeline. By this means the very high velocities that will result in a single bore pipeline, from the expansion of the air, can be prevented. By this means it is often possible to gain a significant increase in performance of the pipeline. The pressure drop in a stepped bore pipeline can be evaluated in exactly the same way as outlined above. A critical point in stepped bore pipelines is the location of the stepsalong the length of the pipeline. At each step in the pipeline the conveying air velocity must not be allowed to fall below a given minimum value, otherwise the pipeline is liable to block at that point. The solution, therefore, is likely to be an iterative one since the velocity of the air at the step depends upon the pressure at the step.

8.5 Minimum conveying air velocityThe conveying line inlet air velocity to be used is the starting point in the design process and a value is based on the minimum conveying air velocity. Once a value is established, together with a conveying line inlet air pressure, the air mass flow rate can be determined so that the operating point can be located.For dilute phase conveying a relatively high conveying air velocity must be maintained to ensure that the material does not drop out of suspension and block the pipeline. This is typically in the region of 10–12 m/s for a very fine powder, to 14–16 m/s for a fine granular material, and beyond for larger particles and higher density materials. For dense phase conveying, air velocities can be down to 3 m/s, and lower in certain circumstances.

8.6 Conveying line inlet air velocityIt is generally recommended that, for design purposes, the pick-up, or conveying line inlet air velocity at the material feed point, should be about 20 per cent greater than the minimum conveying air velocity. This should provide sufficient margin to allow for surges in material flow, air mover characteristics, and other

contingencies. An unnecessarily high conveying air velocity should not be employed as this will have an adverse effect on system performance, in terms of air pressure needed, and hence power requirements. For guidance purposes an approximate value of the pick-up or conveying line inlet air velocity to be employed for pneumatic conveying and so this incorporates the 20 per cent margin. For convenience, materials here are classified as being either ‘floury’ or ‘sandy’. Floury materials are those that are very fine and have good air retention properties and will convey in dense phase in a moving bed type of flow. Sandy materials are typically fine granular materials that have neither air retention nor permeability and so will only convey in dilute phase suspension flow in a conventional pneumatic conveying system. These curves simply represent ‘average’ materials .

9.CONTROLLING SYSTEM

9.1 Air supply controlWith some machines it may not be possible to obtain independent control of flow rate and pressure, and with others it may prove difficult to achieve the potential energy saving. If a general high pressure air supply service is available, choked flow nozzles can be used most effectively to control the air flow rate at a given pressure, but the energy saving will depend upon the air supply system employed. The use of choked flow nozzles . With some pneumatic conveying systems operating with their own self-contained air supply, others using a general service . A comparison of the potential performance and air requirements of a system required to convey different materials over a distance of 200 m. such a wide range of air movers available, each with it own operating characteristics, it is quite impossible to offer general recommendations on system control in this respect.High, low and negative pressure systems all require separate treatment, with control of the air mover being necessary in some cases, and control by means of the air supply line being possible in other cases. The important points to bear in mind are that different materials are quite likely to have different volumetric air flow and power requirements, and that the air supply should be capable of meeting both the maximum demand and being conveniently controlled to lower demand levels.

9.2 Material flow controlSince different materials have different flow rate capabilities in a given conveying line, due consideration should be given to the material feeding device. Changes in material feed rate must clearly be made, for if a design was based on the conveying of material B only, for example, the pipeline would be considerably under-utilized for the conveying of material A. Alternatively, if the design was based on material A, the pipeline would almost certainly block when conveying material B, even if the air flow rate was correct. The feeding device, therefore, should be capable of operating satisfactorily and conveniently over the range to be encountered. With volumetric feeders, such as rotary valves and screws, differences in material bulk densities should also be taken into account as well as differences in flow rate.

9.3 Multiple delivery pointsMany pneumatic conveying systems are required to deliver a material to a number of different locations. For example, by means of diverter valves in a pipeline several hoppers or silos can be loaded from a given supply point. If the delivery points are at varying distances from the supply point, however, it is unlikely that it would be possible to achieve the same material flow rate to each point. With different material flow rates, and hence solids loading ratios, it is possible that air flow rates would also have to be adjusted for a material capable of being conveyed in dense phase.

9.4 Material influencesFor materials capable of being conveyed in dense phase, an increase in conveying distance for a constant conveying line pressure drop will result in a reduction in material flow rate, and so the material will have to be conveyed at a lower solids loading ratio. At a lower value of solids loading ratio a higher minimum conveying air velocity will required, and hence an increase in air flow rate will be necessary.

10. Problem occurred in conventional systemTo fully understand the limitations of this type of feeder the thermodynamic relationships need to be followed and these are presented in Chapter 10. In this it is shown that in a 100 mm bore pipeline, with air supplied at 0.2 bar gauge, the throat diameter would have to be about 36 mm. Although venturis capable of feeding materials into conveying systems with operating pressure drops of 0.3 bar are commercially available, the pressure drop across the venturi can be of the same order. Venturi feeders, however, are yet another type of feeder that can have its operating pressure range extended significantly, should this be required, by means of incorporating the device in a lock hopper system. For an operating pressure drop of 0.3 bar and a 50% energy recover rate in the venture this means that the air supply will have to be at about 0.6 bar gauge and consequently the air will have to be supplied by a positive displacement blower. Since there are no moving parts these feeders are potentially suitable for abrasive and friable materials. A particular advantage of the venture feeder, compared with many other feeding devices, is that it is small, occupies little space, and can be relatively cheap. It also requires very little headroom, which is often of benefit where pneumatic conveying systems may need to be fitted into existing plant with little room for modifications.

11.VENTURI FEEDER

COMPONENTS OF PROJECT

Centrifugal Blower

Power Rating 680W Discharge Rate 2.8m3/min RPM 16000rev/min

Conveying pipes

Pipe Materials - Mild Steel Diameter - 65 mm Length - 5 m Application - To Carry powder Materials

Throat

There are 3 Throat pipe of Diameter20mm 25 mm 30 mm

Differential Manometer

Capable of measuring pressure Difference between conveying pipe to throat. Water and Air Mixture is Use.

HOPPER

No of Hopper -: One Shape-: Conical Use-: Feed the Powder Material From Hopper to Venturi

SOCKET

No of Socket-: 2 Material- : Mild steel Use- : Made Connection between Venturi & Conveying Pipes .

Valve

No of Valve-: One Use-: Regulate the air flow by Air Blower

Base

Air Blower Pneumatic Pipes Venturi Manometer all Placed on the Base Which made of Ply Wood..

STEP OF WORKING PROCESS

Pipe Cutting Cut the Pipe into many Pieces for the fabrication of Pneumatic system.

Threading

Threading is done on the Lathe Machine Threading is use to couple venturi to main conveying line. Pitch of thread:- 3mm Thread:-V thread

Processing of venturi

Sheet metal Cutting for manufacturing of venturi's Convergent and Divergent Part.

Sheet Metal Development

Drawing on sheet metal Cut Sheet according to Drawing Bent Sheet into Conical Sh Now weld to form convergent and divergent shape.

Drawing

Drawing is made by geometrical instrument(pencil , scale compass , protector).

1st venturi detail:-

1. Length of converge part:-55mm2. Diameter of throat:-20mm3. Length of throat:-45mm4. Length of divergent part:-90 mm

2nd venturi detail:-1. Length of converge part:-90 mm2. Length of throat:-85mm3. Length of divergent part:-130 mm4. Diameter of throat:-25mm

3rd venturi detail:-1. Length of converge part:-45 mm2. Length of throat:-85 mm3. Length of divergent part:-60 mm4. Diameter of throat:-30mm

How we fix the length of venturi part. The venturi for the pull push type conveying system designed considering general considerations :- Convergent cone venturi has a total included angle of 21°±1°. Divergent cone has a total included angle lying between 5° to 15°. Diameter of throat varies from 1/3 to ¾ of the pipe diameter(Generally ½ times diameter of pipe). After this consideration we use Pythagoras theorem to calculate the length of converge part and

diverge part.

Drilling on Throat

Drilling on Throat to make a passage to inlet powder material. Another hole for pressure measurement by Manometer.

Fabrication of venturi Welding

Gas welding used to join converging throat & diverging part of venturi.Final shape of venturi

For Suction of Raw Material. Measurement Of Pressure by Manometer.

Fabrication of conveying pipe

Arc welding is used for joining the pipes Mild steel pipe is used for conveying the material.

Final assembly of pneumatic conveying system

All parts of Pneumatic pipes , Venturi joined with the help of Valve and Socket . final Shape Placed on the Bed.

VENTURI FEEDER

Since the basic problem with feeding positive pressure systems is that the air leakage arising from the adverse pressure gradient can interfere with the flow of the material into the pipeline, this situation can be improved, to a certain extent, by using venture feeders. These work on the principle of reducing the pipeline cross-sectional area in the region where the material is fed from the supply hopper, as shown in Figure 3.16.It will be seen that there are no moving parts with this type of feeding device, which has certain advantages with regard to wear problems. There are, however, no inherent means of flow control either, and so this has to be provided additionally. A consequence of the reduction in flow area is an increase in the entraining airvelocity and a corresponding decrease in pressure in this region. With a correctly designed venturi the static pressure at the throat should be the same as that in the supply hopper which, for the majority of applications, is atmospheric pressure. This then encourages the material to flow more readily under gravity into the pipeline, since under these conditions there is no leakage of air in opposition to the material feed. In order to keep the throat at atmospheric pressure, and also of a practical size that will allow the passage of material, and for it to be readily conveyed, a relatively low limit has to be imposed on the air supply pressure. These feeders, therefore, are usually incorporated into systems that are required to convey free flowing materials at low flow rates over short distances.

11.2 Principle of venturi feeder

Venturi feeder work on the principle of reducing the pipeline cross sectional area in the region where the material is fed from the supply hopper .

11.1 Various parameter involved in the system

11.1.1 Flow controlSince experience has shown that these feeders are best suited to the handling of free flowing materials, care must be taken to continuously control the flow of materials, otherwise a blockage may occur. There is no inherent means of flow control, as mentioned earlier, and so this means that the venturi could either be fed from a belt, screw, rotary valve or vibratory feeder. Alternatively a supply hopper could be used if fitted with a trickle valve, calibrated orifice plate or gate/slide valve.

11.1.2 Suction nozzlesA specific application of vacuum conveying systems is the pneumatic conveying of bulk particulate materials from open storage and stockpiles, where the top surface of the material is accessible. Vacuum systems can be used most effectively for the offloading of ships and for the transfer of materials from open piles to storage hoppers. They are particularly useful for cleaning processes such as the removal of materialspillages and dust accumulations. In this role they are very similar to the domestic vacuum cleaner. For industrial applications with powdered and granular materials, however, the suction nozzles are rather more complex. It is essential with suction nozzles to avoid filling the inlet tube solidly with material, and to maintain an adequate flow of air through the conveying line at all times. To avoid blocking the inlet pipe, sufficient air must be available at the material feed point, even if the suction nozzle is buried deep into the bulk solid material. Indeed, the vacuum off-loading system must be able to operate continuously with the nozzle buried in the material in order to maximise the material flow rate. Sufficient air must also be available for conveying the material through the pipeline once it is drawn into the inlet pipe. In order to obtain maximum output through a vacuum line it is necessary to maintain as uniform a feed to the line as possible with the absolute minimum of pulsations. To satisfy these requirements two air inlets are generally required, one at the material pick-up point and another at a point downstream.

11.1.3 Feed rate controlThe conveying pipeline is provided with an outer sleeve at its end, and primary air for material feed is directed to the conveying line inlet in the annular space created. The length ‘a’ of this sleeve has to be long enough to ensure that it is not buried by the movement of the material and so prevent the flow of primary air. There should not be a risk of an avalanche of material from covering the air inlet at the top of the sleeve either. This sleeve may be many metres long for a ship off-loading application.

11.1.4 Hopper off-loadingIn this application the nozzle is usually positioned close to the bottom of the hopper. The vacuum nozzle is generally fitted into the hopper via an external sleeve so that it can be easily removed when required. The controls over the primary and secondary air are also arranged to be external to the hopper. The location of the control for positioning the outer sleeve with respect to the conveying pipeline can also be external to the hopper. For these reasons a section of flexible hose is often incorporated into the conveying pipeline close to the hopper.

1st venturi detail:-5. Length of converge part:-55mm6. Diameter of throat:-20mm7. Length of throat:-45mm8. Length of divergent part:-90 mm

2nd venturi detail:-5. Length of converge part:-90 mm6. Length of throat:-85mm7. Length of divergent part:-130 mm8. Diameter of throat:-25mm

3rd venturi detail:-5. Length of converge part:-45 mm6. Length of throat:-85 mm7. Length of divergent part:-60 mm8. Diameter of throat:-30mm

How we fix the length of venturi part. The venturi for the pull push type conveying system designed considering general considerations :- Convergent cone venturi has a total included angle of 21°±1°.

Divergent cone has a total included angle lying between 5° to 15°. Diameter of throat varies from 1/3 to ¾ of the pipe diameter(Generally ½ times diameter of pipe). After this consideration we use Pythagoras theorem to calculate the length of converge part and

diverge part.Operation involved in venturi

Sheet metal development

Drawing on sheet metal Cut Sheet according to Drawing Bent Sheet into Conical Shape.

Now weld to form convergent and divergent shapFabrication of venturi

Gas welding used to join converging throat & diverging part of venturi.

Final shape of venture

For Suction of Raw Material. Measurement Of Pressure by Manometer.

Experimental analysis on venture Reading

Venturi Blower opening

Head at inlet of system(cm)

Pressure at inlet

Head at throat of system(cm)

System 1 1 57 1.069 12.9

3/4 55.1 1.067 15.5

1/2 37.5 1.049 33.5

System 2 1 61.3 1.073 8.5

3/4 55 1.067 15.5

1/2 43.2 1.055 27.1

System 3 1 53.4 1.065 17.2

3/4 48 1.060 22.4

1/2 36.1 1.048 34.3

1/2 O

pening

3/4 O

pening

Full o

pening0.92

0.94

0.96

0.98

1

1.02

1.04

1.06

1.08

1.049

1.068 1.069

10.993

0.974000000000001

SYSTEM 01

Inlet PressureThroat Pressure

1/2 O

pening

3/4 O

pening

Full O

pening0.94

0.96

0.98

1

1.02

1.04

1.06

1.08

1.055

1.0671.073

1.0050.998

0.992

SYSTEM 02

Inlet PressureThroat Pressure

1/2 O

pening

3/4 O

pening

Full O

pening0.94

0.96

0.98

1

1.02

1.04

1.06

1.08

1.048

1.061.065

0.996 0.996 0.994

SYSTEM 03

Inlet PressureThroat Pressure

Comparison of Different Venturi System

It is clear the graph that suction at the throat section increases with the blower opening. According to Graph, maximum suction pressure develop for system 1. It is maximum for full opening i.e. at full discharge.

Advantage to Other Conveying System

The main advantage of pneumatic conveying system is that material is transferred in close loop, there by preventing the environmental effect on the material and vice versa.

In pneumatic conveying, power consumption is a function of the system design, transfer rate, and convey length.

Because compressed air is injected along the convey pipeline, the system automatically adjusts the compressed air distribution to break plugs when they occur.

As there are less moving parts so less wear and tear as compare to Belt Pulley System. Applications:-

The applications of pneumatic conveying systems can be seen in many industrial sectors. A list of industrial fields where it has extensively been used is given below

Chemical process industry Pharmaceutical industry Mining industry Agricultural industry Mineral industry Food processing industry

CONCLUSION The main objective of the work was to use venturi-feeding system for the pull push type pneumatic conveying system, thereby developing the suction effect at the venturi throat. This will help to create the automatic suction of the material into the system through the inlet provided at the throat. This system then can be operated by the single person and has numerous practical applications for the automatic transportation of powdered and granular material.

MATERIAL DISCHARGE METHODS

Material typically exits via filter receivers or cyclone separators. Positive pressure systems can additionally employ fill/pass valves to discharge material from the system at one use point, or redirect the material to another use point.

Filter Receivers

Filter receivers separate solids from the air stream using filter media and gravity, and are generally specified when materials contain smaller particles that are prone to dusting and/or when dust containment is

a primary requirement. They are normally located above material use points, and employ reverse-pulse jet filter cleaning to dislodge accumulated dust from filter surfaces, allowing continuous and efficient

separation of material from the air stream. These can be used in both pressure and vacuum systems.

Cyclone Separators

Cyclones operate by generating a vortex of particulate laden air. Centrifugal force pushes the particulates toward the outer cyclone wall where they lose velocity and spiral downward to the discharge. The relatively particulate-free air is then exhausted through the clean air discharge port which is attached to the top of the cyclone. Filters of various types and with various methods of solids recovery are used to clean up the transport gas before discharge or recycle.

Fill/Pass Valves

Fill/pass valves are commonly used to discharge material directly into individual or multiple process vessels and/or to deliver it to several destinations along a common conveying line. Downstream of the last fill/pass valve, the conveying line is normally routed to the original material source point or into a dust collection device. It is used only in pressure systems.

Directly Into Process Vessels

Both pressure and vacuum systems can feed material directly into blenders, reactors and other enclosed process vessels that are vented to a downstream bag house or other dust collection device, eliminating the need for individual filter receivers. It can be used in both pressure and vacuum systems.

PERFORMANCE OF THE SYSTEM

Ways to Increase Capacity

1. Optimize solids/air ratio

2. Minimize the number of bends

3. Shorten the total conveying distance

4. Reduce conveying velocities to just above saltation

5. Step up the line diameter near the end of the system

• Doing so decreases the total system pressure drop

6. Minimize flex hose length and eliminate where possible

Ways to Minimize Wear in Conveying Lines

1. Reduce conveying velocities

2. Use wear resistant materials for more prevalent abrasive materials - Sand, carbon black, etc.

3. Minimize line length and number of bends

4. Enter the vessel radially, not tangentially

5. Hang a flapper in the middle of the bin to allow the material to contact it instead of the vessel wall

6. Step up the line diameter before the vessel entrance

Top Ten Tips for Dilute Phase Pneumatic Conveying

1. Do not use sloping pipe runs. The refluxation, (run-back and re-conveying of the same material), will require the pipe to re-transfer the product slipping back on top of its normal load, and the effect is accumulative. At best it will significantly increase the conveying burden, but is more than likely tend to block the lower bend.

2. Allow a 'reasonable' horizontal conveying length before the first bend to allow the bulk material to accelerate to a stable conveying speed and reduce the sectional loading of the conveying pipe. Material slowed by the bend occupies a greater proportion of the pipe’s cross sectional area and thereby offers more obstruction to the air flow, which increases the pressure drop along the system.

3. Do not fit bends close together on the pipe run for reasons similar to the above.

4. Consider stepping the pipeline on long runs. Air expands with pressure drop, so velocities inevitably increase along a constant pipe run. Higher material velocities increase wear on bends and product degradation.

5. 'More air' can be 'less transfer capacity' in dilute phase systems. Larger solids and gas frictional losses caused by higher gas velocities can absorb more energy than the extra input of energy. There is an optimum gas flow rate for a given lean phase flow system. Check with a specialist for the correct solids/gas ratio balance and top performance.

6. Product damage and wear at bends is very material dependent. Blind Tee does usually have much merit, but cause a higher pressure drop than long radius bends.

7. Rotary valves do leak and also pass air differentials through the returning empty pockets. They also tend to fill with product on one side of the valve as the empty pockets are rotated to present a space for material to flow in. Back flow of gas and biases intake causes many feed problems. Make sure that the valve is properly vented and that the feed channel is of good form for flow across the whole cross section. A short inlet standpipe is useful for such duties as a cyclone outlet or a feed into a high pressure line.

8. Check that cyclones have an unobstructed outlet. If there is intermittent or periodic discharge, allow clear buffer capacity to avoid interfering with the cyclone operation.

9. Allow for the pressure drop on the supply line to the blower. Include an allowance for any filter, silencer, acoustic box or compressor enclosure and extended supply run, as may be appropriate. Be sure to compensate for the temperature increase due to gas compression.

10. Provide adequate instrumentation; this is essential to know what is going on and to facilitate a proper investigation of any problems that may arise.