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Specialization: Transport Engineering and Logistics Report number: 2013.TEL.7760
Title: Bulk handling equipment for grain
Author: A.N.M. van der Bijl
Title (in Dutch) Uitrusting voor op en overslag van graan als stortgoed
Assignment: Literature Confidential: No
Supervisor: prof.ir J.C. Rijsenbrij
Delft University of Technology
FACULTY OF MECHANICAL, MARITIME AND MATERIALS ENGINEERING
Department of Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl
Student: A.N.M. van der Bijl Assignment type: Literature Supervisor (TUD): Prof. ir J.C. Rijsenbrij Creditpoints (EC): 10
Specialization: TEL
Report number: 2013.TEL.7760 Confidential: No
Subject: Bulk handling equipment for grain
Grains are agricultural products and are one of the world’s most important food products. Grains are produced and used throughout the entire world. The global trade in grain measures hundreds of million tons each year. Most grain is transported as loose bulk; over the years this has resulted in specially designed handling equipment.
For this literature study you should focus on the equipment, applied for the handling of grain in the entire transport chain. In this assignment you are asked to:
Identify all handling steps for grain bulk, from the first transport up to the final delivery to a trader or a factory.
For each handling step, give the options available for fulfilling the job.
Give various criteria for the assessment of the bulk handling equipment.
Present alternatives for unitized transport of grain instead of loose bulk.
Based on your literature survey, it is expected that you will come up with a clear overview of the bulk handling equipment used for grain. The report should comply with the guidelines of the section. Details can be found on the website.
The professor,
Summary
This report is about all handling steps involved in the transport cycle that bulk grain undergoes in their journey from crop to shop. This contains truck, train and ship transportation including loading and un-loading, the types of storage, internal transport and unit transportation. Grains are granular products like: wheat, corn, rice, beans etcetera. These are world’s most important food products, the worldwide production is about 2350 million tonnes and the trade is over 295 million tonnes per year. This makes the handling of grain in bulk very important.
For all the steps various types of equipment are available, this literature study is done to give an overview of the market and to give a basis for the assessment of the different types of equipment. Basic criteria for the assessment are: the field of application; the working principle; capacity(range); operational con-ditions; material deterioration; contamination and cost (both investment and annual cost).
In all steps of the transport cycle a first deviation can be made by the way the material is transferred: continuous or discontinuous, in other words with a constant massflow of the grain in bulk or in batches. Continuous systems are for example conveyor based (un)loaders, discontinuous systems are mostly crane based.
Transportation of grain per truck is great for relative small quantities and is very flexible. Trucks are often used at the start of the transportation cycle and for the final delivery. Truck configurations vary per country due to different legislation in allowed weight and size. Trucks are loaded by a hopper mounted above the road or by shovel loaders. The unloading of trucks can be done by the trucks itself or by external equipment. Self unloading is done by tilting their load, or by opening hatches in the bottom to discharge above a hopper. Delivering the material directly to a silo can be done by a pneumatic or screw discharge system, this makes the truck ideal for final transportation. The external unloading equipment tilts the entire trailer over an angle resulting in discharge of the truck from the back, the advantage is that no equipment has to be driven around, resulting in a higher payload.
Trains are less flexible than trucks but have a larger capacity and this makes them ideal for longer dis-tances with larger loads. Grain transportation by rail is basically always done by hopper shaped wagons, it can also be done by simple rectangular wagons. The most common way to load a train is by a hopper mounted above the rail. Bottom unloading is the most applied method of unloading, since most grain is transported in hopper shaped wagons. Hatches at the bottom of the wagons are opened to let the bulk flow out of the wagon into a hopper under the track. Rectangular wagons are emptied by turning them over.
When a lot of grain needs to be transported over a long distance, ships are the best way, the economy of scale results in a low cost per ton per kilometer. Shiploading on some small scale terminals is done by excavators or shovel loaders maybe with the help of a conveyor, most shiploading is however done continuously. By means of internal transport the grain bulk arrives at the shiploader, by simple chutes or pipes the material can slide into the ship’s holds. It is important to reach all the holds of the ship and all areas and corners of the holds. Either the shiploader boom is able to reach all places or with the help of chutes or a Jetslinger the hold gets adequately filled.
Unloading ships is an large energy demanding step due to the quick vertical unloading of the grain from the ship’s holds. The deviation between continuous and discontinuous unloading is obvious: continuous unloaders versus all types of cranes. The continuous unloaders used for grain bulk are: screw type, twin belt, chainconveyors and pneumatic unloaders. A screw conveyor uses a rotating helical shaped blade to get the material upwards. Twin belt is in fact a normal conveyor belt only covered by another conveyor belt to keep the material from falling of. A chainconveyor uses a moving chain with attached plates inside
a box to lift the bulk material. Pneumatic unloaders use a difference in air pressure to suck the material from the holds, these unloaders are considered to be non mechanical due to the lack of moving parts in contact with the bulk. Each unloader has its own advantage, some have a very good cleanup efficiency, others have lower yearly cost, a detailed analysis on the individual project is necessary to make a fair choice. Discontinuous unloading is done by cranes, there are various types available on the market: dou-ble boom cranes, luffing and fixed boom cranes and gantry cranes. Depending on the required capacity and on the infrastructure available there is a crane available for each job.
Storage of the grain in bulk is often necessary because the incoming material flow at the terminal does not match the outgoing flow at the same moment. Depending on the required storage capacity and the required frequency of storage a terminal can use different types of storage. A main distinction is open, covered or enclosed storage. Grains are often stored in covered or closed facilities to protect the material. Open storage is simply putting the grain bulk on a stack, this can be the most simple way but with the help of highly automated machines and infrastructure this can be a large scale solution as well. Covered storage is simply putting a roof over the stack to prevent the bulk against weather influences. An even better way to protect the grain and the environment is enclosed storage in silos. A way to compare the different ways of storage is the area utilisation, in metric tons per square meter.
Internal transport is all transport on site or on a terminal. This can be done by conveyors as discussed before, other possibilities are a bucket elevator or a tubular drag conveyor. A bucket elevator is used to gain height, a chain or belt with buckets attached to it takes the material upwards. Enclosed tubular drag conveyors realise a completely enclosed way of transport, the material is pulled through a pipe by a chain with flanges, the route is not bound to straight lines. Internal transport can also be done discontinuously by trucks or shovel loaders.
Unit transportation is becoming more popular, it allows the bulk to be transported in a more practical way instead of loose bulk. Containerized and bagged transport are very common nowadays especially for shorter distances and/or for smaller quantities. There are various ways to fill a container, it is possible to tilt the container and load it from the top, or to fill the container in a horizontal position from the back. Unloading of a container can be done by tilting or by a pneumatic unloading system similar to truck unloading. Flexible Intermediate Bulk Containers known as big bags are used to transport batches of approximately one ton. The big advantage of bigbags is that empty bigbags require very little space compared to a container. Small 25 or 50 kilogram bags are also used to transport grains, especially rice since this is already an end product. Special shiploaders with a chute are used to load the small bags into the ship’s hold.
The eventual choice of the type of equipment for every step in the crop to shop cycle depends on many factors, it is therefore not possible to point out one best type of equipment per step. Further investigation into the detailed application and use is necessary. It is up to the user which criteria are most important and then a choice should be made. This report gives an overview of the various possibilities.
Samenvatting
Dit rapport betreft alle middelen in de transportcyclus van graan als stortgoed, vanaf de oogst tot aan de winkel. Dit omvat het transport met vrachtwagens, treinen en schepen, inclusief het laden en lossen; opslag; intern transport en eenheden transport. Granen zijn korrelvorige agrarische producten zoals: tarwe, rijst, bonen en mais. Dit zijn ’s werelds meest belangrijke voedsel producten, waarvan jaarlijks 2350 miljoen ton wordt geproduceerd en 295 miljoen ton internationaal wordt verhandeld. Dit maakt de uitrusting voor dit stortgoed erg belangrijk.
Voor elke stap in de cyclus zijn verschillende soorten machines beschikbaar. Deze literatuurstudie is gedaan om een overzicht te geven van de markt, daarnaast biedt dit rapport een basis voor de beoordel-ing van deze machines. Basis criteria hiervoor zijn: toepassbeoordel-ingsgebied; werkbeoordel-ingsprincipe; capaciteit; operationele voorwaarden; product verval en kosten (zowel investerings- als jaarlijkse kosten).
In elke stap van de transportcyclus kan allereerst onderscheid gemaakt worden in de manier van product verplaatsing: continu of discontinu, een constante massastroom of bulk in batches. Continue system zijn bijvoorbeeld gebaseerd op transportbanden, terwijl discontinue system vaak zijn gebaseerd op kranen. Transport van graan per vrachtwagen is zeer geschikt voor kleine hoeveelheden en is erg flexibel. Vracht-wagens worden veelal gebruikt in het begin en het eind van de transportcyclus. Vrachtwagen configu-raties verschillen per land door de verschillen in wetgeving voor toegestane massa en afmeting. Vracht-wagens worden geladen door een trechter boven de weg of door middel van shovels. Het lossen van vrachtwagens kan door de vrachtwagens zelf gedaan worden of met externe hulp. Het zelfstandig lossen gebeurt door middel van kiepen of het openen van luiken in de bodem boven een trechter. Het stortgoed kan ook met behulp van een pneumatisch of schroef systeem direct aan een silo worden geleverd, dit maakt de vrachtwagen ideaal voor transport naar de eindbestemming. Het lossen met externe hulp wordt gedaan door de hele vrachtwagen te kantelen. Het voordeel hiervan is dat er geen los installatie op de vrachtwagen is geinstalleerd waardoor deze een grotere vracht mee kan nemen..
Treinen zijn minder flexibel dan vrachtwagens maar hebben een grotere capaciteit, waardoor ze veel toegepast worden voor grotere lasten en langere afstanden. Graan transport over rails wordt over het al-gemeen gedaan met conisch gevormde wagons, het is echter ook mogelijk graan in simpele rechthoekige wagons te vervoeren. Wagons worden meestal behulp van een trechter boven de rails. Het lossen van wagons gebeurt meestal door luiken in de bodem aangezien de meeste graanwagons conisch gevormd zijn. Onder de rails bevindt zich een stortbak, door het openen van de luiken komt het stortgoed in de stortbak terecht vanwaar het verder getransporteerd wordt. Vierkante wagons worden gelost door ze om te draaien.
Schepen worden gebruikt voor het transport van zeer grote hoeveelheden graan over een grote afstand, de kosten per ton per kilometer zijn laag. Schepen laden wordt op kleinere terminals gedaan met kranen en shovels, eventueel met behulp van een transportband; de meeste scheepsbelading wordt echter continu gedaan. Door middel van intern transport komt het stortgoed aan bij de scheepsbelader, via buizen en goten kan het materiaal het scheepsruim in glijden. Het is belangrijk dat elk ruim van het schip en elk hoekje van het ruim goed gevuld wordt; dit kan door middel van bewegende scheepsbeladers of met be-hulp van glijbanen of ”Jetslingers”. Jetslingers kunnen het materiaal alle hoeken van het ruim inschieten. Schepen lossen is een van de meest energie vragende handelingen in de cyclus van het graan. Het ver-schil tussen continu en discontinu is hier erg goed zichtbaar: continue tegenover allerlei soorten kranen. Continue scheepslossers zijn gebaseerd op: schroef, dubbele band, ketting en pneumatiek systemen. Een schroeflosser maakt gebruik van een roterend schroefvormig blad om het materiaal omhoog te brengen. De dubbele transportband heeft in feite twee tegen elkaar gedrukte transportbanden die zo het materiaal
vasthouden en omhoog bewegen. Een ketting transporteur bestaat uit een buis met daarin een omhoog bewegende ketting waaraan platen zijn bevestigd, en trekt zo het materiaal mee. Pneumatische lossers gebruiken een verschil in luchtdruk om als het ware het stortgoed mee te zuigen. Elke losser heeft zijn eigen voordelen, sommige zijn erg zuinig, ander hebben hele goede leeg kwaliteiten of lage jaarlijkse kosten. Afhankelijk van een specifiek onderzoek naar de individuele toepassing kan pas een goede keuze gemaakt worden.
Discontinu lossen wordt gedaan door kranen, er zijn verschillende types op de markt beschikbaar: dubbele giek kranen, kranen met vaste giek of toppende giek en portaal kranen. Afhankelijk van de gewenste capaciteit en de beschikbare infrastructuur is er een geschikte kraan voor elk doel.
Opslag van granen is vaak nodig omdat op een terminal de inkomende massa stroom niet gelijk is aan de uitgaande massa stroom op dat moment. Afhankelijk van de behoefte aan capaciteit en de frequentie dat opslag nodig is kan een terminal kiezen voor verschillende soorten opslag. Het grootste verschil is gegeven door: open, overdekt of afgesloten opslag. Open opslag komt neer op ruwweg materiaal storten op een berg, dit kan erg simpel zijn maar met geautomatiseerde machines en een goede infrastructuur is erg grootschalige opslag mogelijk. Overdekte opslag is hetzelfde als open opslag alleen is de berg nu overdekt en wordt beschermd tegen weersinvloeden. Een nog betere manier om de granen en de omgev-ing tegen elkaar te beschermen is door compleet afgesloten opslag in silos. Een goede indicatie om silos te vergelijken is oppervlaktegebruik, uitgedrukt in het aantal tonnen dat per vierkante meter opgeslagen kan worden.
Intern transport is al het transport op locatie of op een terminal. Dit kan gedaan worden door trans-portmiddelen zoals al eerder beschreven voor scheepslossers maar er zijn meerdere mogelijkheden. Om hoogteverschillen te overbruggen bestaan emmer-elevatoren: een ketting of band waaraan emmers beves-tigd zijn neemt het materiaal mee omhoog. Gesloten buistransporteurs hebben een ketting met flenzen welke het materiaal door een buis trekken. Het voordeel van dit systeem is dat het niet gebonden is aan rechte lijnen.
Eenheden transport wordt steeds populairder, hierdoor kan het stortgoed op een meer praktische manier vervoerd worden dan als los stortgoed. Het transport in containers en bigbags is tegenwoordig zeer ge-bruikelijk, vooral voor kleinere hoeveelheden en/of voor korte afstanden. Er zijn verschillende manier om een container te vullen, men kan de container kantelen en vanaf boven vullen, of de container kan horizontaal blijven en vanaf de achterkant volledig gevuld worden.
De uiteindelijke keus voor het middel voor elke stap in de transportcyclus van graan hangt af van vele factoren, daarom is het niet mogelijk om een beste middel aan te wijzen voor elke stap. De gebruiker moet zelf afwegen welke criteria het belangrijkst zijn en een eigen keuze maken. Dit rapport geeft een overzicht van de verschillende mogelijkheden.
Contents
1 Introduction 9
2 Grain 11
2.1 Properties . . . 11
2.2 Production and trade . . . 11
3 Equipment Characteristics 13 3.1 Field of application . . . 13 3.2 Working principle . . . 13 3.3 Capacity (range) . . . 13 3.4 Operational conditions . . . 13 3.5 Material deterioration . . . 14 3.6 Contamination . . . 14 3.7 Costs . . . 14 3.7.1 Operational efficiency . . . 14 4 Trucks 15 4.1 Truck configurations . . . 15 4.2 Truck Loading . . . 15 4.3 Truck Unloading . . . 17 4.3.1 Self unloading . . . 17
4.3.2 Separate unloading equipment . . . 19
5 Trains 20 5.1 Train Wagons . . . 20
5.2 Train Loading . . . 21
5.2.1 Load out station . . . 21
5.2.2 Separate equipment . . . 22 5.3 Train unloading . . . 22 5.3.1 Bottom unloading . . . 22 5.3.2 Top unloading . . . 22 6 Ships 24 6.1 Ship loading . . . 24 6.1.1 Continuous loading . . . 24 6.1.2 Mobile loader . . . 25 6.2 Ship unloading . . . 27 6.2.1 Continuous Unloading . . . 27 6.2.2 Discontinuous Unloading . . . 32 6.2.3 Energy Consumption . . . 35
CONTENTS CONTENTS 7 Storage 36 7.1 Pile storage . . . 36 7.1.1 Area utilisation . . . 36 7.1.2 Stacker reclaimer . . . 38 7.2 Open storage . . . 38 7.3 Covered storage . . . 39 7.4 Enclosed storage . . . 39 7.5 Blending . . . 40 8 Internal Transport 42 8.1 Continuous internal transport . . . 42
8.1.1 Bucket elevator . . . 43
8.1.2 Enclosed tubular drag conveyor . . . 43
8.2 Discontinuous internal transport . . . 43
9 Unit transport 45 9.1 Containerized . . . 45
9.1.1 Horizontal loading . . . 45
9.1.2 Tilted container loading . . . 45
9.2 Bagging . . . 47
9.2.1 Bigbags . . . 47
9.2.2 Small bags . . . 48
Chapter 1
Introduction
This report is made to give an overview and a certain insight into the various types of equipment available for the handling of grain in bulk. Grain bulk is defined as bulk with granular particles and this report focusses on agricultural bulk only. Handling is defined as all transport steps from crop to shop, in other words all steps involved in the journey of the grains from the truck leaving the farmer or trader, up to the delivery to the final trader or factory. This contains the following steps in chronological order:
• Trucks, loading and unloading • Trains, loading and unloading • Ships, loading and unloading • Storage of the grains
• Internal transport • Unit transport
All these separate steps in the chain have their own needs and demands, this means that most operations use different equipment. In this report all steps of the crop to shop cycle will be dealt with in a separate chapter. As stated in the literature study of Gratema [Gratema(2005)] a lot is known about the ports but very little about the equipment installed. There are a lot of different machines available on the market, but just little is known about the variety and deviating possibilities. How does the various equipment work and can they compete with others? This report should give a clear overview and help to compare and assess the various types of equipments used within one of these steps with it competitors. The comparison mainly focusses on these characteristics:
• Field of application • Working principle • Capacity • Operational conditions • Material deterioration • Contamination • Costs • Efficiency
CHAPTER 1. INTRODUCTION
Together these characteristics should give a good overview of the differences between the various equip-ment and should therefore help one to get a first insight when searching for the appropriate grain handling equipment.
This study is relevant and useful because the subject concerns ways of transporting food, people all over the world depend on the trade of food, it is vital! An enormous amount of agribulk is traded around the world, this requires a lot of the handling equipment and makes this literature study therefore relevant. As Gratema stated: ”A lot of know how about the functionality and facilities for bulk terminals has been collected. More research is however recommended concerning the applied equipment and systems for additional functions” [Gratema(2005)].
Chapter 2
Grain
Before getting into more detail of all handling steps of grain in bulk a little more knowledge of the bulk grain material is admirable. This chapter is about the properties of grain and about the production and trade of grain. This knowledge makes it easier to understand the equipment designs discussed further in this report.
2.1
Properties
The grains discussed in this report are considered to be granular agricultural product, also called cereals, some examples of grain are: wheat, soybeans, corn(maize), sunflower seeds, rice and barley. Table 2.1 gives some examples with their values for the density and angle of repose. The angle of repose is the angle of the slope of a pile material relative to the horizontal plane. These two values are important for the design of equipment, the density determines the load on the equipment and thereby the required strength and the angle of repose is important for flowing and storing of the grain material. For simplicity for the rest of this report the density for grain is taken to be 0,75 ton per cubic meter and the angle of repose is 28 degrees.
Table 2.1: Grain characteristics
Type Density[ton/m3] Angle of repose[degrees]
Wheat 0,77 25
Soybeans 0,763 25
Corn 0,72 23
Barley 0,61 28
sources: [Dobraszczyk(2001)]; [Paul(2001)]; [Wyatt(2002)].
The quality of a batch of grain material is defined by a lot of factors divided over three categories: physical, sanitary and intrinsic [Maier(1995)]. Physical factors are for example: moisture content, ker-nel size and weigh and amount of damaged kerker-nels. Sanitary factors are: insects, toxic materials and dust. Intrinsic factors are: oil content, protein content, hardness, density and feed value. Some of these factors can be influenced during handling, especially damaging kernels, change in moisture content and contamination are liable to happen. Of course this should be avoided or at least kept to an acceptable minimum.
2.2
Production and trade
The Food and Agriculture Organization of the United Nations estimates that the world production of cereals in 2011/2012 was approximately 2350 million tonnes and the trade of cereals in the same year
2.2. PRODUCTION AND TRADE CHAPTER 2. GRAIN
was 295 million tonnes [Food and Agriculture Organization(2012)]. This gigantic amount of bulk has to be transported all over the world which makes the equipment essential. According to the Food and Agriculture organisation, has the total world usage of cereals risen the last 10 years from 1753 million tonnes in 2001/2002 to 2324 million tonnes in 2011/2012 this is an increase of 32 percent. The world trade of grain has also risen more than 30 percent. This increase in trade obviously demands more from the trading companies and the equipment used. With upcoming economies like China and Africa further market growth seems very likely.
Chapter 3
Equipment Characteristics
This chapter explains the criteria which are important for the assessment of the various types of equip-ment. Not every criterium is applicable for every step in the crop to shop cycle, however these are the main criteria which should give a clear and good first impression of the differences of the various types of equipment. Of course it depends on the user or buyer to add suitable weightfactors to the different criteria to be able to find the best equipment for every specific use. The characteristics will be shortly explained in the following sections.
3.1
Field of application
To be able to compare the different types of equipment one has to know the equipment at least fulfills the same job, for instance loading, unloading or both. The application also concerns which materials the equipment can handle.
3.2
Working principle
The working principle seems in first sight not important for the choice of equipment, they are however very distinctive and are therefore also taken into account. The working principles are in fact the main deviation between the various types of equipment. Due to experience with a certain principle or when it has proven itself, the owner trust it and tends to choose it again. In every chapter the working principle will be the guideline in explaining the equipment.
3.3
Capacity (range)
The capacity is one of the most important criteria, obviously the equipment has to fulfill the requirements of the user. The capacity is given in ton/hr or sometimes in cubic meter per hour which can be calculated into tons per hour. A rather low capacity per unit equipment might result in a large number of needed equipment, the advantage is that it is very flexible to adopt to the needed capacity by putting the exact needed number of equipment to work. The disadvantage is the economy of scale, for example every machine has to be put to work by men, resulting in an often higher workload resulting in higher variable costs. Equipment with a too large capacity i.e. overcapacity, means that most of the time the equipment might be too expensive for the job.
3.4
Operational conditions
The operational conditions concern the circumstances under which the equipment is used. Amongst others the required personnel, the needed power supply and the infrastructure needed for the equipment.
3.5. MATERIAL DETERIORATION CHAPTER 3. EQUIPMENT CHARACTERISTICS
Obviously this results in cost but this also involves the location, environment, climate etcetera. Some-times it is just not possible to built the entire infrastructure or to get men to work 24/7 at a specific location, therefore it is very important to keep this in mind when assessing equipment.
3.5
Material deterioration
The deterioration of the material is about the damage a machine can do to some types of bulk, this makes equipment not suitable for all types of grain bulks. This does not need to concern the buyer if he installs the equipment for just one specific product, but for a multi material terminal this might be important and should be taken into account.
3.6
Contamination
The risk of contamination exists of two parts, contamination of the bulk itself and contamination by the bulk into the environment. The bulk can be contaminated by for instance hydraulic oil leaking from a crane or has to be protected against the weather outside. Contamination of the environment can for example occur through dust. This also involves preventing dust explosions. Some types of equipment are completely enclosed and therefore reduce contamination enormously, depending on the type of terminal, location, legislation and type of bulk this may be very important.
3.7
Costs
The cost of the equipment is very important to the investor, of course this has two sides, the investment costs and the annual cost. The investment costs consist of the purchase of the equipment, but also the infrastructure needed for the equipment has to be paid for, this contains the foundation, the powersupply and installation costs. The annual costs are very important for the assessment as well, these are built up by the involved labour costs, energy usage and maintenance costs. Together these two costs are an indication for the variable as well as the fixed costs. A low priced machine might turn out to be very expensive in use. Energy efficient machines are often more expensive to buy, due to more expensive drives, but are often cheaper in the annual costs due to lower energy consumption. This shows that this consideration is very important. The lifetime of the equipment should also be noted here.
3.7.1 Operational efficiency
Operational efficiency is the ratio between operational capacity versus technical capacity. This is espe-cially of interest for shipunloading and concerns the ability of the equipment to keep a constant unloading rate, even when the holds are almost empty, Some types of equipment have a very high maximum capac-ity but are dependent on small excavators to clear the last part of a ship’s hold and thereby reducing their capacity dramatically. This means despite the efficient unloader, additional work is required and thereby increasing the total unloading cost.
Chapter 4
Trucks
The chain ’from crop to shop’ starts at a local storage facility where the grain enters the transport cycle. For large distances and large quantities grains are transported by ships, but of course not all transportation of grain bulk can be done by ships because it is simply not possible to reach all places by waterways. Besides that it is also not economical to transport small amounts by ship. Therefore a lot of grain is transported to and from bulk terminals by different means, mainly trains and trucks. This chapter will deal with the truck transport and focusses mainly on loading and unloading. The next chapter is about the train transportation
4.1
Truck configurations
Before explaining the loading and unloading options of the trucks it is necessary to know something about the various types of trucks, here several basic configurations will be discussed. Note that this chapter only concerns with the loose bulk transport; there is a separate chapter about the unit transport like containers and bags (chapter 9 Unit Transport). The most common truck configurations are:
- Truck with an additional wagon (figure 4.1) - Truck semi-trailer combination (figure 4.2) - Truck with double trailer (figure 4.3)
It depends on the hauling company which type of truck suits his purposes, but the location is very impor-tant because the allowable size and weight of trucks vary per country due to the differences in legislation. For example in the Netherland the allowed maximum weight is 50 ton and the maximum length is 18,75 meter [Rijksoverheid(2013)](with a special permit 60 ton and 25,25 meter length is allowed). To give an indication of the capacity: assume a width of 2,2 meter, 12 meter length and a loading height of 2,5 meter; with a density of 0,75 for bulk grain this is a load of 49.5 ton and this does not include the own weight of the truck. This indicates that not the vehicle dimensions are limiting but the allowed weight is. As stated this differs per country, in Europe the maximum allowed weight is most often 40 tonnes with some exceptions to 44, 50 or even 60 tonnes[Forum(2011)].
4.2
Truck Loading
The most common way to load a truck is either by hopper shaped silos or by shovel loaders. Loading by a silo means that a silo is mounted above the road to make it possible for the truck to drive underneath it, by opening at the bottom of the silo the truck is filled. The loading by hopper shaped silos is even more applied in train loading, therefore it is discusses in more detail in section 5.2, Train Loading. Loading can also be done discontinuously by shovel loaders also called wheel- or mobile loaders or similar equipment like forklifts trucks. The loading by shovel loaders is largely applied in smaller terminals or when the transhipment of grain is only temporarily. Loading by shovel loaders is simply picking up the material
4.2. TRUCK LOADING CHAPTER 4. TRUCKS
Figure 4.1: Truck with wagon, Hoogland B.V.
Figure 4.2: Truck trailer combination
4.3. TRUCK UNLOADING CHAPTER 4. TRUCKS
Figure 4.4: Truck loading by Shovel loader, by Volvo
from the stack and dumping it in the trailer. Sometimes to reduce the height difference between the shovel loader and the top of the trailer a ramp is used. Some well known manufacturers of shovel loaders are: Caterpillar, Liebherr, Komatsu, Volvo and Werklust. Figure 4.4 shows loading of a truck by a shovel loader.
4.3
Truck Unloading
As stated previously it deviates per country what type of truck is used and thereby also the common types of unloading deviates. To unload a truck there are various options: unloading by the truck itself or with help of separate equipment. A self unloading truck may be equipped with a tilting mechanism, a discharge bottom or a pneumatic or screw discharge mechanism. The decision to not equip the truck with unloading equipment can be made to reduce the weight of the truck and thereby increasing the payload. This becomes more interesting for larger distances or for standardised routes with equipment installed. A self unloading truck is obviously more flexible.
4.3.1 Self unloading
The truck itself may be equipped with a discharge system, this can be bottom unloading, tilting, or discharging with pneumatics or screws.
Bottom unloading
For bottom unloading special trailers are necessary, these trailers must be hopper shaped and have a hatch at the bottom. Grain material has a rather low angle of repose (approximately 28 degrees), therefore with a hopper angle which is at least this angle the material can flow out once the hatch at the bottom of the trailer is opened. Figure 4.5 shows a drawing of this type of trailer, this one is manufactured by Timpte has a hopper angle of 31 degrees[Timpte(2011)]. At the unloading site a hopper is mounted underneath the surface, called a pit, this hopper leads to a conveyor which takes the bulk to storage or the next transport. When a full trailer is above the pit the hatch is opened and the grain flows into the hopper, see figure 4.6. Well known manufacturers of this type of trailers in the USA and Canada are amongst others Timpte and Lode King.
4.3. TRUCK UNLOADING CHAPTER 4. TRUCKS
Figure 4.5: Bottom unloading trailer by Timpte
4.3. TRUCK UNLOADING CHAPTER 4. TRUCKS
Tilting
Another way of unloading is tilting; lorries and trailers are often equipped with hydraulic cylinders to make it possible to tilt their load, similar to a dump truck. This means that dropping the bulk from an entire trailer at a small area is possible, it can be directly emptied on a stockpile or in a hopper from where a conveyor takes care of the further transport.
Discharge equipment
A lorry or trailer may also be equipped with discharge equipment, this means the grain material is not just dumped on the surface or into a pit but is moved directly to where it needs to be. Walinga is amongst others a producer of discharge equipment, they make trucks with a screw or chain in the bottom to transport the grain material to the back of the truck from where the material is transported by a screw conveyor or by pneumatic system [Walinga(2012)]. This makes it possible to, for example, fill a silo with grain by air pressure. It is also possible to do this without a chain or screw in the bottom of the trailer, then the trailer should be tilted to move the material towards the pneumatic device. The self unloading equipment makes it possible to deliver small quantities to end users.
4.3.2 Separate unloading equipment
Some trailers are specially designed for maximum capacity this means no bottom discharge or tilting equipment is installed at the truck itself there is only a door or hatch at the back of the trailer. To empty this type of trucks, the trailer, with or without truck, is put on a so called tipping platform or truck dumper. This platform tilts the entire trailer over an angle, resulting in emptying from the back. Figure 4.7 illustrates this type of unloading. This type of unloading is largely applied in the field of high volume transport of low density materials like wood chips but can also be applied for biomass or even grains [Bruks(2012b)]. The maximum load can be as much as 100 tons and the platform can be tilted over an angle up to 63 degrees [Megatech Engineering(2012)] which is more than enough for grain since the angle of repose is only 28 degrees.
Chapter 5
Trains
Transport by rail is especially practical for larger quantities over long distances, both domestic as well as international. Trains are great for connecting the large ports with the big traders and customers. This chapter is about the loading and unloading of trains, of course some knowledge about train wagons is needed therefore this will be discussed first. Same yields as for trucks, only the transport of loose bulk is discussed here.
5.1
Train Wagons
Large scale bulk transport by train can be done by basically two types of wagons: hopper shaped wagons as displayed in figure 5.1 and simple rectangular wagons see figure 5.2. Many grain wagons are covered to prevent the material against weather influences. Greenbrier is a manufacturer of both types of wagons and produces hopper shaped rail wagons with a capacity of up to 186 m3 per wagon [Greenbrier(2012)].
Figure 5.1: Hopper shaped grain wagon by Greenbrier
5.2. TRAIN LOADING CHAPTER 5. TRAINS
Figure 5.3: Bateman Load Out station
5.2
Train Loading
Train loading can be done by a load out station or with a separate equipment like shovel loaders with or without the help of an conveyorbelt. For train loading it does not matter what type of wagon is used, it is however important if the wagons need to be filled through hatches or if the top is open. If the wagons needs to be filled though hatches a load out station is very practical, shovel loaders can also fulfill the job but need help of a conveyor.
5.2.1 Load out station
The load out station is the most applied method of train loading. The material is stored in a hopper above the rail, the train can simply drive underneath the hopper and is filled by opening the hatch of the hopper, this is called a load out station or loading station; see figure 5.3 for an example. Often the required unloading capacity of the hopper at certain times is much higher then the capacity of the internal transport medium responsible for filling the hopper. This means that during train loading, the internal transport can not keep up with the unloading rate of the hopper, therefore depending on the required output measured in wagons per hour, a silo is installed above the hopper to compensate for this deviation. This makes sure the entire train can be loaded in an acceptable short time. Bateman is a well known producer of this train loading stations [Bateman(2012)].
5.3. TRAIN UNLOADING CHAPTER 5. TRAINS
Figure 5.4: Mobile loader constructed by N.M. Heilig b.v.
5.2.2 Separate equipment
Depending on the site the trains can also be loaded by a conveyor belt connected directly to a reclaimer or loaded by a shovel loader or crane. Because the capacity of the conveyorbelt or cranes are now the limiting factor it might be slower then loading with a load out station. For smaller sites it is rather common to load wagons directly with a shovel loader. This of course reduces the investment costs for a terminal drastically but does mean the capacity is quite low. Figure 5.4 displays a mobile loader, this machine can be loaded by simple shovel loaders and conveys the grain into a train wagon, this is also useful equipment for truck and barge loading
5.3
Train unloading
After reaching its destination the train has to unload its cargo. There are basically two ways of unloading, considering only bulk cars, no containers. The first type of unloading is through the bottom of the wagons, the second option is unloading from the top. Top unloading is not much used for grain, more for coal and iron ore but will be discussed since it is a very distinctive way of unloading and is possible for grain transport.
5.3.1 Bottom unloading
For bottom unloading special wagons are necessary; these are the hopper shaped wagons of figure 5.1 and have hatches underneath. As for the trailers as discussed in section 4.3 truck unloading, the hopper must have a higher angle than the angle of repose of the grain to guarantee that the bulk will flow out. At the site is an unloading station with a hopper mounted underneath the track. When a full wagon is above the pit the hatch of the wagon is opened and the grain flows into the hopper, from the hopper the material gets transferred further, see figure 5.5. This process can be done with a constant speed of the train throughout the unloading station.
5.3.2 Top unloading
Top unloading is designed for wagons with no hatches at the bottom, like the wagons of figure 5.2. This way of unloading means more work in the unloading station, an entire wagon (or two at once) is turned over or tilted to empty it. The advantage of this method is that emptying can be done faster and that
5.3. TRAIN UNLOADING CHAPTER 5. TRAINS
Figure 5.5: Unloading station by Loeweneu Engineering
bulk wagons do not need to be hopper shaped but can be a rectangular box, which is more economic for transportation. Especially when there is very strict legislation for a limited train length this becomes interesting. The disadvantage is the huge investment costs for this large installation. Figure 5.6 shows an example of top unloading of a coal wagon.
Chapter 6
Ships
Ships are the main transport modality for the transportation of large quantities of grain over large dis-tances. Ships have an enormous capacity and due to the economy of scale they can realise the lowest cost per ton per kilometer.
There are various sizes of bulk carriers available on the market. The most common ship sizes used for grain handling goes up to Panamax size. Panamax size is specified by the limitations of the Panama canal and locks: maximum width of 32,31 meter, length of 289,56 meter and a maximum draft of 12,04 meter [Autoridad del Canal de Panama(2005)]. This size of vessel is very common because the USA is one of the major importers and exporters of grain and to be able to go to Europe as well as Asia in a short sailing time the ships should be able to pass the Panama canal. Currently is worked on additional larger locks at the Panama canal, the width of the lock will be 55 meter, the draft will be 18,3 meter and the new length will be 427 meter, this will allow larger ships, the question is whether the grain traders will change their ships, because this might also influence the equipment used at terminals.
6.1
Ship loading
Ship loading is in fact similar to truck loading, however in practice the difference in load capacity results in different equipment. Most loading of ships is continuously through conveyors and chutes. In some small terminals loading is done by conveyors and cranes sometimes combined with a mobile loader. Obviously besides the user and terminal preferences the choice of equipment depends largely on the size of ships and barges to load and the frequency the loading has to occur.
6.1.1 Continuous loading
If a site is equipped with a good infrastructure of conveyors and a reclaimer system, then often the ships are loaded continuously. The internal transport which will be discusses in chapter 8 takes the material to the shiploader. The bulk can arrive on ground level at the shiploader, meaning the loader also does the vertical transport, or the grain bulk can arrive at a high point from which the loader only has to drop or slide the material into the ship’s hold.
The shiploader can be a combination of belts and chutes or, when dust prevention or material protec-tion is important, this can also be done by an enclosed system, depending on the capacity, for example a covered high capacity conveyorbelt or a totally enclosed screw conveyor.
A shiploader can be mounted in various ways: fixed, luffing, slewing, travelling or a combination of the above [Bruks(2012a)]. It is important that the installation can reach all holds of the ship. Obviously a fixed loader is not very flexible and the ship has to move to ensure successful filling, luffing means the outreach of the loader can vary, slewing is the rotation of the loader’s boom and travelling means the en-tire loader can travel on the quay alongside the ship. Obviously a combination results in the best loading
6.1. SHIP LOADING CHAPTER 6. SHIPS
Figure 6.1: Telescopic chute with dust covers, by Telestack
possibilities, but this comes at a price, the installation is more expensive or in case of a traveling loader the entire quay has to be stronger, requiring better and more expensive infrastructure. Figure 6.1 shows a smaller type of a travelling, luffing bargeloader. Neuero is an example of a producer of shiploaders, they built loaders with a capacity up to 3000 ton/hr capable of loading post Panamax vessels [Neuero(2012)].
Chute options
The chute of a shiploader can have various options, for example these can be dust reducing or guarantee better filling of a hold. The last part of dropping the material in the hold can be dust free if one uses a telescopic chute with a dust cover which reaches onto the pile see figure 6.1. A so called ”Jet Slinger” is a device that can be used to spread the material over the entire hold, it uses a belt to shoot the ma-terial in a certain direction. Techniplan makes jet slingers with a capacity up to 1000ton/hour for grain [Techniplan(2012)]. A jet slinger has a bypass to let the material flow straight into the hold, only when it is necessary to reach the corners the jet slinger is in function. An example of a jet slinger is given in fig-ure 6.2. More efficient filling can also be realised with a sliding chute under the chute of the shiploader, this sliding chute should be rotatable to reach all sides and corners.
6.1.2 Mobile loader
Mobile shiploaders are conveyor based loaders, with a hopper or receiving unit for trucks or shovel load-ers to drop off the grain bulk. An example of a mobile shiploader is displayed in figure 6.3, this mobile loader uses trucks for receiving the product. As visible in the same figure this system can be com-pletely covered to prevent dust and protect the product against the environment. This mobile shiploader is produced by BW, and is has a capacity up to 2000 ton per hour [BW part of Aumund Group(2012)]. Because the mobile shiploader is tire mounted it can travel throughout the terminal making them very flexible and with an outreach up to 27,5 meters even Capesize Vessels can be loaded.
6.1. SHIP LOADING CHAPTER 6. SHIPS
Figure 6.2: Jet-Slinger by Aumund
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
6.2
Ship unloading
In this part the different processes of unloading a ship in a port will be discussed. The biggest challenge in shipunloading is lifting the material vertically out of the ship’s hold. Clearly due to the gravity and the internal angle of friction of the grain material the bulk won’t come out on itself. To maintain a good overview the deviation of the different types of unloaders has the same structure as used in the report Bulk handling in ports[Willekes(1999)]. The unloading processes can be divided into two main groups: continuous and discontinuous unloading. Table 6.1 at the end of this chapter shows a summary of all stated data concerning the various types of shipunloaders to give a clear overview.
6.2.1 Continuous Unloading
Continuous unloading, as the word indicates, is a continuous process, this means a constant flow of materials. In practice continuous unloading can again be divided into two parts, pneumatic driven and mechanical driven equipment. The pneumatic driven unloading equipment is a rather small group which consists of mainly vacuum pumps to suck the grain out of the vessel and blow it into a silo, train, cart or another vessel. The mechanical driven continuous unloading equipment involves a broader scope of unloaders. There are unloaders bases on a screws, buckets, chains and belts. The equipment available in both parts will be worked out into more detail.
Screw Unloader
A rather common known and largely applied continuous unloader is the screw unloader. This is an un-loader of the mechanical type and uses a screw conveyor to lift the material from the ship’s hold, the principle is displayed in figure 6.4.
The basic principle of the screw conveyor is a very old invention done by Archimedes somewhere in 235-240 B.C. The design has remained basically the same ever since [Lodewijks(2011a)].The screw conveyor’s mechanism is based on a rotating blade with a helical shape inside a tube. Through the ro-tational motion around the axle, the material inside the tube gets pushed in the axial direction. More special is the inlet of the screw conveyor displayed in figure 6.5. It can be seen that through the rotation of the outertube the bulk is pushed downwards towards the inlet, there the screw with an opposite rota-tional direction takes up the material. Connecting several tubes and by using joints a complete enclosed conveying system from the ship’s hold to the quay is realised. From the quay the bulk can be transported to where it needs to be: transhipment, storage, truck or train.
The main advantages of the screw conveyor unloading is the that totally enclosed transport is possi-ble, which result in no contamination of the bulk into the environment or vice versa. A disadvantage of the screw conveyor is the wear on the blades and the wall resulting in maintenance costs. Worldwide market leader in screwconveyors is Siwertell, part of the Cargotec group. Siwertell makes road mobile, stationary and travelling screw unloaders; with a capacity range from 240 up to 2400 metric tons per hour [Cargotec(2012b)] [Cargotec(2012a)]. Due to the moving blade and more friction to the wall, material deterioration is more likely to occur.
Twin Belt
The twin belt system is an alternative for the screw unloader, it is also a mechanical continuous unloading system but based on a conveying belt. Basically it is a normal loaded conveyorbelt only there is another belt laying on top of the bulk to enclose it, see figure 6.6. This ensures that during vertical transport the bulk will not fall down. The three illustrations in figure 6.6 shows the principle of the two belts, empty, partly filled and completely filled. This example comes from the Simporter system manufactured by Vigan, Vigan uses rollers and air pressure to keep the two belts together [Vigan(2012)]. The belts are
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
Figure 6.4: Screw Conveyor
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
Figure 6.6: Simporter Twinbelt principle, by Vigan
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
filled using a paddle wheel, figure 6.7. The paddle wheel is located at bottom of the belts, by rotating it swings the bulk into the opening between the two belts. Subsequently the belts clamp together around the bulk and takes it up. Neuero is another company manufacturing such a system, called Multibelt with a capacity range from 600 to 1200 ton/hr, the energy demand is approximately 330 kW [Neuero(2005)], 0,275 kWh/t.
Chain conveyor
The chain conveyor also known as ”en-masse conveyor” has a lot of similarities with the twin belt or multibelt principle, it is another mechanical continuous unloader. A chain conveyor consists of a vertical box or tube, inside this box runs a chain with plates(flanges) attached to it. The chain has an upwards motion inside the box and because the plates are mounted perpendicular to the chain direction the plates lift the material. One of the main suppliers in the world of chain conveyors is Buhler. They built small barge unloaders with a capacity of 150-300 ton per hour (bargolink). But also big equipment (portalink) with a capacity range of 440-1200 ton/hour for grain bulk [Buhler(2012)]. The energy consumption is not given for all types of chain unloaders, only one value is given for a medium range unloader: 0,3 kWh per metric ton, for a 330 ton/hour unloader. It is assumed that the energy consumption is equal for all chain unloaders from Buhler.
Bucket
Gratema studied all bulk ports between le Havre and Hamburg [Gratema(2005)], his study showed that for agribulk unloading no bucketelevators or bucketwheel unloaders are used. Buckets unloaders are used for coal and iron ore unloading. However a short explanation of the principles of these continuous unloading machines is given here because it is a possibility to unload ships.
As the words suggest a bucketwheel and a bucketelevator both use buckets to unload a ship. The bucket elevator uses buckets attached to a chain to dig up the material and lift it out of the ship’s hold. The bucketwheel unloader uses one big wheel with buckets attached to it. The buckets scoop up the material at the bottom and drop the bulk on a conveyorbelt when they reach the top of the wheel. The bucketwheel is mainly used for non free flowing materials such as coal or powders. For a comparison the capacity of a bucketelevator can be as high as 8000 metric tons of iron ore per hour [Takraf(2007)]. The density of iron ore can be about 4 times larger than grain, this means if a bucketelevator can keep the same volume discharge for grain it is possible to unload 2000 ton per hour.
Pneumatic
A very distinctive type of unloading is pneumatic unloading. This is continuous unloading but this is not considered mechanical, because there is no mechanical device shoving or scooping out the material. As the word suggests a pneumatic unloader uses a pressure difference in air, resulting in an airflow, to get the materials out of the ship’s hold. The working principle is rather simple and can be compared to the venturi effect. A pipe is lowered into the bulk material, the end of this pipe is called the nozzle and is in fact a pipe in a pipe. The outer pipe has an overpressure, delivering the airflow to the material, the airflow leaves through the inner pipe which has a lower pressure, the airflow sucks the bulkmaterial with it, see figure 6.8.
Pneumatic unloaders are available with a hanging suction pipe, not movable with respect to the main boom, and with a movable suction pipe to be able to reach more places inside the hold. The equipment can be wheel based and movable but can also be railmounted, portal mounted or mounted at a fixed loca-tion. In general the pneumatic unloaders have a high operational efficiency, is able to reach most places in the hold and has good cleaning capacities without the help of additional equipment. A drawback is that pneumatic unloaders have a relative high energy consumption, modern equipment uses about 0,6-0,8 kWh per ton grain [de Visscher(2007)]. There are various suppliers of this equipment for instance:
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
Buhler, Neuero, Walinga and Vigan. The capacity varies from 170 up to at least 800 metric tons per hour.
Figure 6.8: Pneumatic unloader
Comparison continuous unloaders
A report form the Technical University of Munich concerning the energy efficiency in bulk material handling industry contains an comparison of the life cycle cost for continuous grain unloaders with a capacity of 600 ton per hour [Rakitsch(2012)]. This shows that after 30 service years the total life-cycle costs differ a lot. A pneumatic unloader is the cheapest in purchase with 1,7 million euros versus 2,6 for a screw unloader and 2,5 for a chain unloader. But after 30 years the total cost (including maintenance and powerconsumption) is by far most expensive for a pneumatic unloader with over 10 million euro, while a screw conveyor cost approximately 9 million euro and a chain unloader less than 8 million euro, see figure 6.9.This same report showed that the average energy efficiency of a pneumatic system was only 60 percent, compared with 80 percent for a chain type, 75 for a screw type and 65 for a belt type system.
Figure 6.9: Cost comparison continuous 660t/hr unloaders, source: [Rakitsch(2012)]
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
versus mechanical unloaders, however due to the better cleanup properties of the pneumatic unloader the total cost might be less, depending on the properties of the ship’s hold and the terminal requirements. Detailed analysing of a project is necessary to be able to make a good choice.
6.2.2 Discontinuous Unloading
A completely different type of unloading is discontinuous unloading, this is in fact all crane based un-loading. Of course there are still a lot of various types of cranes: mobile cranes, fixed and luffing cranes and gantry cranes. All with their own (dis)advantages. Basically the principle of crane unloading is to grab as much bulk material as the crane can handle, lift it out of the ship’s hold and take it to shore. Often onshore is a hopper which drops the material on a conveyor for further transport; of course the material can also be dropped in a cart, truck, train or storage place directly.
A drawback of all cranes is that they can not guarantee enclosed transport at all times, this means there can be dust and there are possibilities for contamination of the bulk material.
Double Boom Cranes
This type of cranes is defined by the way it lifts the load, opposite to all the other cranes this crane does not use a winch and cables to lift the grab from the ship’s hold, but uses a second boom instead, see figure 6.10. The grab is directly attached to the crane’s boom, this has the advantage that it is possible to place the grab precisely where the operator wants it and that he can use the boom to push the grab into the bulk material to completely fill the grab. A major drawback of this type of crane is that it is not suitable for very large ships, the booms are simply not large enough to be able to cover the entire ship. Sennebogen and Mantsinen are well know manufacturers of this types of cranes, with a effective lifting capacity of up to 25 ton(at 20 meters) [Mantsinen(2012)].
Luffing and fixed boom Cranes
These types of cranes use a winch with a grab to unload the ships. The cranes have a large boom to make sure the grab can reach far enough to unload the entire ship. The difference between luffing cranes and fixed boom cranes is in the boom: as the words suggest the boom is fixed for a fixed boom crane, this means the crane has to rotate to get a certain outreach. The luffing crane can move the tip of the boom, by doing this it can change its outreach to reach the entire ship’s hold without slewing, see figure 6.11. Fixed boom cranes are mostly railmounted to compensate for the low degrees of freedom of the boom. Luffing cranes can be railmounted or tyremounted to be mobile and flexible, but can also be mounted on a fixed position if that is sufficient for the terminal. The cranes can also be mounted on a barge, this has the advantage that they can be used throughout the entire port and that the terminal does not need to have a strong quay to support the crane. Gottwald an Liebherr are famous for their mobile harbour cranes, both produce mainly luffing cranes. Gottwald offers different sizes of cranes up to a capacity of 1850 ton/hour [Gottwald(2012)]. Liebherr states that with their Pactronic efficient lifting system they can reach a capacity of 2000 ton/hour [Liebherr(2012)].
A special type of luffing cranes are level luffing cranes, also called lemniscate cranes and double link level luffing cranes. These cranes are able to luff without changing the height of the load, this means when luffing the load only undergoes a horizontal trajectory, resulting in lower energy consumption. NKM Noell is one of the manufacturers of this types of cranes, figure 6.12 shows a level luffing crane. Gantry Cranes
Gantry cranes are the most expensive cranes simply because they require more steel and installations. A gantry crane is in fact a huge portal structure which reaches out over the ship’s holds. The structure is designed in such a way that a trolley can move over the portal from the seaside to the landside, as visible
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
Figure 6.10: Double boom ship unloader by Sennebogen
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
Figure 6.12: Level luffing crane by Figee
Figure 6.13: Gantry bulk unloading crane
in figure 6.13. A winch system is attached to this trolley, which operates the grab. The entire gantry crane can move sideways over a rail, alongside the ship. Due to the gigantic structure compared to the other types of cranes, this crane is capable of handling bigger loads in each unloading cycle, resulting in very large capacities [Tenova(2012)]. Examples of gantry crane manufacturers are Kone cranes, Tenova and ZPMC.
Often a hopper is installed at the base of the gantry crane, this ensures quick unloading of the grab. The conveyors or trucks underneath the hopper take care of further distribution. These hoppers may be equipped with a dust reducing installation and a weighing system.
A drawback of all winch cranes is that they cannot reach the entire surface of the ship’s hold. This means, for example, that loaders have to be put in the hold to bring the material from the corners to a central place which the crane can reach, resulting in a lower unloading efficiency. The so called free digging capacity is very high but due to the poor clean up properties the overall capacity is lower.
6.2. SHIP UNLOADING CHAPTER 6. SHIPS
6.2.3 Energy Consumption
The difference in energy consumption of different types of ship unloading equipment was not found purely for grain bulk, however there has been a study by the Technical University of Munich about the energy consumption for coal unloading. In that study the grab gantry crane is compared with a screwun-loader and a bucketelevator [Gunthner(2010)]. The specific energy consumption (kWh/t) is compared for various unloader capacities. The results show that gantry cranes (with and without energy recovery systems) use lowest energy 0,2 to 0,4 kWh/t, the only screw conveyor tested uses more than 0,5 kWh/t and the bucket elevator was in the middle from 0,25 to 0,35 kWh/t. It has to be noted that there was only one screw unloader tested and that the material is coal and no grain bulk. This should however give a good indication.
Decision Support model
Kok did his masterthesis on a Decision-Support model for agri bulk terminal unloaders from a life-cycle cost perspective [Kok(2008)]. He investigated two cases: an inland barge terminal and an import sea terminal. He concluded that the labour and maintenance are the most important cost drivers, but when high throughput is needed energy consumption is important as well. Slewing cranes are more energy efficient then pneumatic unloaders. Pneumatic and chain unloaders show best performance if only free flowing products are handled. Screw unloaders and grab cranes show reasonable performance for both free flowing and non free flowing products. It depends on the flexibility demands of the terminal in terms of ships size and products which equipment is chosen.
Remarks
Ship size is in this chapter left out of the comparison. This chapter only describes the various basic technical possibilities. For example for barge unloading, special equipment is available based on the same principles.
Ship unloader summary
Table 6.1: Overview Ship Unloaders
Type Capacityrange[t/h] Energy cons.[kWh/t] Purchase[euro] Material
Screw 240-2400 0,5 2600000 All grains
Twin Belt 600-1200 0,275 All grains
Chainconveyor 150-1200 0,3 2500000 All grains
Bucket elevator 2000 0,25-0,35 Coal and ore
Pneumatic 170-800 0,6-0,8 1700000 All grains
Luffing/slewing 750-2000 2400000 All grains
Chapter 7
Storage
Practically always intermediate storage of the grain bulk is necessary between two modes of transport or before the material is used in a factory. By definition if the incoming flow does not match the outgoing flow, storage is needed. Storing may also be done to make profit, the material is stored and one waits for a better price to resell the material.
There are basically three types of storage [Willekes(1999)]: open, covered and enclosed storage, each will be discussed in this chapter. During storage of course one has to make sure the bulk is protected against the influence of the environment but nowadays, due to the environmental regulation, the envi-ronment also has to be protected against the stored bulk, for example dust. Of course the size of needed storage is very important in the choice of the storage type and the equipment installed. An important factor for comparing storage types is the area utilisation or footprint, in tons per square meter, this is especially interesting for high price areas or companies with limited space. Table 7.1 at the end of the chapter shows the footprint values for all types of storage discussed in this chapter.
7.1
Pile storage
The simplest way to store bulk is to store the grains on piles, this is very common, one drops the material from a certain point and underneath a pile is formed. The slope of the pile is equal to the angle of repose, the width of the pile and the height are therefore linked. As expected when one moves the drop-off point then the pile can expanded. It is assumed that for this section all bulk material is delivered by a conveyor belt. When the drop-off point is moved longitudinal to the conveyorbelt a long stockpile can be formed. By making the drop off boom rotating one can make a stockpile at each side of the conveyor belt, see figure 7.1. The drop-off point can also circulating around a certain fixed pole this results in a circular stockpile. The step of dropping the bulk material on a pile is called stacking.
Pile storage can be open as well as covered as will be discussed later in this chapter. This type of storing can be very basic and is used as small intermediate storage for a trader, by simply using dump trucks to stack and shovel loaders to load the material, it can however also be very sophisticated as described in next subsection. The slope of the stockpiles depends on the angle of repose of the material, resulting in a triangular pile, with a limited area utilisation. This can be improved by for example digging a trench for the material or use walls to create higher, but not wider, stockpiles. The walls can be permanently constructed or temporarily built with large building blocks as displayed in figure 7.2.
7.1.1 Area utilisation
If the bulk is stacked on a flat surface, as displayed in the top of figure 7.3, the area utilisation is solely based on the angle of repose(a) and the width(b) of the pile. The average area utilisation is equal to 0,25xtan(a)x(b) times the density(0,75 ton/m3). With an average angle of repose of 28 degrees and an
7.1. PILE STORAGE CHAPTER 7. STORAGE
Figure 7.1: Covered longitudinal stockpile, source [Woodbine(2011)]
7.2. OPEN STORAGE CHAPTER 7. STORAGE
Figure 7.3: Top: flat stockpile, bottom: walled stockpile
assumed pile width of 20 meters this is equal to 2,0 ton/m2. Figure 7.3 also shows the big influence of walls on the area utilisation, adding walls of 2 meter to the same stockpile results in an area utilisation of 3,5 ton/m2.
7.1.2 Stacker reclaimer
Often when the previous described type of storage is used there is a stacker reclaimer system, this means that the bulk is dropped onto the pile by the stacker, often a conveyorbelt. The reclaimer, as the word suggests, reclaims the material form the pile and gets it onto the conveyor system. This combination of stacker and reclaimer and the conveying infrastructure ensures efficient and possibly automated large scale storing. There are two ways of reclaiming: frontal reclaiming and side reclaiming. Frontal reclaim-ing is startreclaim-ing from one side and collectreclaim-ing full cross section slices at once usreclaim-ing a huge reclaimreclaim-ing rack. Side reclaiming is using a sort of conveyor to scrape of small slices from the top to the bottom and then move sideways, showed in figure 7.4.
The material can also be taken from the pile by mobile loaders, cranes or by use of a conveyor or ploughwheel underneath the stockpile. If the last option is used one has to make sure the material flows to the conveyor, this means the pile is not on flat ground but on a trough shaped floor, this also increases the area utilisation.
7.2
Open storage
Open storage is in fact storing the bulk in huge outdoor piles. For big storage plants a stacker-reclaimer system is necessary and a large infrastructure of conveyors has to make sure the bulk can reach any stack and is connected to unloading and loading points of ships, trains and trucks. If the storage is not that big one might be able to handle the bulk material with loose equipment like cranes and shovel loaders. There is no covering or building installed to protect the bulk or the environment, this makes
7.3. COVERED STORAGE CHAPTER 7. STORAGE
Figure 7.4: Side reclaiming, source [Wintz(2012)]
this a very cheap way of storing. Especially for coal and iron this is a ideal way of storing, however for grain bulk it depends on the climate and regulations. If the grain does not need to be protected against the environmental influences like rain and if there is no regulation about the contamination of the environment due to dust, open storage is a good option.
7.3
Covered storage
Covered storage is needed when the bulk needs to be protected against weather influences like water or sun. Basically covered storage is just putting a roof over the piles, see figure 7.1 as an illustration.
7.4
Enclosed storage
Enclosed storage is necessary to protect the bulk against climatic influences like temperature and mois-ture and when the bulk may harm the environment. An example of enclosed storage are silos. Another advantage of silos is that by using height, one can achieve a very high area utilisation.
Silos
GSI is world leader in hopper based steel grain storage bins and builds silos up to a capacity of 36,8 thousand cubic meters with a diameter of only 41,2 meters [GSI(2011)]. This results in an area utilisation of 10,4 ton per square meter. This types of silos are made for flowing materials like grain bulk, the bottom is hopper shaped to ensure the material can come out, figure 7.5 shows this type of silos. For non free flowing materials like flower and powders other types of silos are necessary, these silos must be equipped with a reclaimer to get the material out of the silo, this can be from the bottom or from the top. Eurosilo is one of the producers of these type of silos specifically designed for powders and even sticky bulk [Eurosilo(2012)]. Very wide grain silos are equipped with a reclaimer system at the bottom because it would take too much height to make it hopper shaped. These reclaimers are mostly screw based. GSI also makes this types of silos called grain bins with a flat bottom and a maximum content of 41165 cubic meter, with a diameter of only 41,15 meters the area utilisations becomes 23,21 ton/m3.
7.5. BLENDING CHAPTER 7. STORAGE
Figure 7.5: Grain storage in silo’s by GSI
Figure 7.6: Grain bag loading by Grainlogix
Grain bag storage
A development initiated in the agriculture is grain bag storage, see figure 7.6. A grain bag is a large polyethylene bag with sizes up to approximately 3,6 x 150 meter, and is able to hold up to 546 cubic meters [Loftness(2012)]. This bags are an alternative for silos because it is also enclosed storage. The grain bags are air tight, keeping the material in a good condition. Because these bags lay on the field and are not built in height they have a bad area utilisation but it might be an option for cheap temporary enclosed storage. The price is approximately 1,5 euro per cubic meter for the bag.
7.5
Blending
Blending is not a way to store bulk, but is an option which comes with storing. Although one single product is of the same type it does not mean that it always has homogeneous characteristics, not even within a single batch, not to mention the differences between two completely different loads. The bulk material may have to be mixed to get better consistency in the properties: moisture, grain size, quality etcetera. One can use storage to mix the bulk, this is called blending or homogenising and can be done in various ways. This is not too important at the start of the transport cycle, but it is very important for the end user to guarantee a constant quality.
