Design & comparison of open storage and closed storage system; Ontwerp en vergelijking van open en gesloten kolen opslag systemen

(1)

Delft University of Technology 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

Specialization:

Transportation Engineering and

Logistics

Report

Number:

2016.TEL.8052

Title:

Design & comparison of open storage

and closed storage system

Author

A.E. Alangara Napoleon

Title(in Dutch):

Ontwerp en vergelijking van open en

gesloten kolen opslag systemen

Assignment:

Research

Confidential:

No

Initiator (University)

Prof. dr. ir. G. Lodewijks

Initiator (Company)

ESI Eurosilo B.V

Supervisor:

Dr. ir. D.L. Schott

(2)

Delft University of Technology 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.E.Alangara Napoleon Assignment type: Design Supervisor: Dr. ir. Dingena Schott Report number:

Confidential: 2016.TEL.8052 Yes Specialization: TEL

Creditpoints (EC): 15

Subject: Design & comparison of open storage and closed storage system

At power plants, coal is stored in open stockyards to create a buffer and blend before fed into the power plant boilers. Coal is affected by the environmental conditions and there is physical and qualitative loss of coal due to wind, rains and spontaneous combustion. Issues like land acquisition and stricter environmental norms have increased the pressure on power plant owners to look at closed storage system as an alternative.

The assignment is to design the open storage and closed storage systems (mammoth silos) on a conceptual basis for a particular design requirement. The evaluation of the solutions shall be based on Environmental Management Accounting (EMA).

The research should cover the following tasks.

1. Choose the appropriate design option for different functions in the open and closed storage system.

2. Identify the design requirements for which the storage systems should be designed.

3. Design the concepts of the open stockyard with associated equipment and closed stockyard with associated equipment.

4. Based on EMA, compare the solutions and critically present your analysis.

The design requirements shall be the choice of the student. The report should comply with the guidelines of the section. Details can be found on the website.

The mentor,

(3)

i

Prologue

This research assignment report is being submitted as a part of the curriculum for final year of Transport Engineering and Logistics, Faculty of Mechanical Engineering at Delft University of Technology. The research assignment has been completed in collaboration with ESI Eurosilo B.V, The Netherlands. I would like to thank Prof. dr. ir. G. Lodewijks (TU Delft) and Mr. J.P.J. Ruijgrok (ESI Eurosilo B.V) jointly for giving me the opportunity to work on this assignment. I would also like to thank my supervisors Dr. ir. D. L. Schott (TU Delft) and Mr. R. Spaargaren (ESI Eurosilo B.V) for all their help, immense support and guidance to complete my research assignment.

Furthermore, I would like to thank Mr. Henri de Boer (ESI Eurosilo B.V), Mr. Chris Geijs(ESI Eurosilo B.V) for their efforts in helping me, providing information and answering my questions patiently.

(4)

ii

Summary

In the event of recent changes in environmental norms in India, India’s biggest power producer, National Thermal Power Corporation (NTPC) has been facing heat regarding the pollution created by its coal based power plants (Centre for Science and Environment, 2015). Another pressing issue faced by NTPC is the land availability, wherein securing adequate empty land for new power plants as well as inadequate land for augmenting the system (SAIKIA, 2013). The conventional method of storing coal in Indian power plants as huge open stockpiles has been questioned in the recent past. As Eurosilo system (closed storage) has been gaining wide popularity in the world market for its use in coal storage, a feasibility study is being conducted comparing the closed storage system with the conventional open storage system used in India for a specific case scenario.

The purpose of this report is to showcase the feasibility of the closed storage systems on the basis of Environmental Management Accounting (EMA) (United Nations Division for Sustainable Development, 2001) (Schott, 2007). EMA compares the initial costs, annual costs and the end of life costs and enables to make a comprehensive analysis on the life cycle cost of the systems. The analysis is done by making a conceptual design of the systems, drawing the basic specifications and arriving at the costs of the system. The first step is formulating the design criteria based on the coal requirement of the power plant and other statutory design requirements. Delft systems approach (Hans P.M. Veeke, 2008) is followed to perform a methodical approach to the selection of the system design for both open and closed storage systems. Once the system design of the open and closed storage systems are fixed, the basic specifications of the open and closed storage systems are formulated to satisfy the design criteria and the delft systems methods.

The estimation of installation cost for both open stockyard system and the Eurosilo system has been done on a budgetary basis on consultation with a number of equipment suppliers and industrial experience. The annual costs have been calculated based on literature, interviews with power plant owners, regulatory authorities and such. The cost heads as per EMA have been filled to the extent possible to enumerate the annual costs of the system. It is evident that the capital cost including IDC(interest during construction) of the enclosed stockyard system is higher than that of the open stockyard system by INR 1,894,029,100. However the annual running costs of the Eurosilo system is comparatively lesser to the open stockyard system coupled with many benefits such as lesser power consumption, lesser consumption of resources like water, fuel, lesser footprint and zero pollution. Considering the above, such extra installation cost could be recovered around 5 years of operation of the plant.

It has been identified that amongst all the factors influencing the cost recovery period, the civil cost of the system influences the installation cost and the loss of coal influences the annual running costs. The storage requirement which depends on the powerplant capacity and the coal quality, not to mention the soil characteristics influences the civil cost of the Eurosilo system while the loss in coal entirely depends on the quality of coal, the environmental conditions, operational excellence of the user. Moreover, the loss of coal in every powerplant would be a point of debate, hence a bandwidth of loss percentages has been considered and the effect of such a bandwith has been analysed. Considering

(5)

1-iii

2.2% of coal losses with respect to the annual coal throughput, it is found that the variation in the

recovery period of the extra investment is from 11 to 3.5years.

In India, it is expected that the coal-based power generation will continue to play a critical role in the next 30–50 years. The policies regarding air pollution and governmental norms with respect to air quality are continually evolving in the recent years. Hence it becomes essential for the thermal power plants to adopt globally proven technologies in the immediate future, to bring a check to the deteriorating air quality. Therefore, at this juncture, adoption of enclosed coal storage system in place of open coal storage would help the thermal power plants meet the stringent environmental norms. In the light of the growing demand for reduction of air pollution, cost of electric power, dependence on generation of power from coal, awareness about the deteriorating environment and upcoming stringent environment norms in India, the biggest advantages of Eurosilo system are that it is eco-friendly and requires less space, less water and other added advantages as discussed in the report. Thus it is inferred from the study that the installation of the Eurosilo system is beneficial to all stakeholders and is a viable option to adopt in the present day industry scenario.

(6)

iv

List of Figures

Figure 1 Innovation model as a design process (Hans P.M. Veeke, 2008, p. 184) . ... 5

Figure 2 Interdisciplinary design approach - Innovation model (Hans P.M. Veeke, 2008, p. 190) . ... 5

Figure 3 Context determination - Stockyard system ... 7

Figure 4 Structure determination - open stockyard system . ... 9

Figure 5 Structure determination - Closed stockyard system . ... 10

Figure 6 System configuration - open stockyard system . ... 16

Figure 7 System configuration - Closed stockyard system . ... 17

Figure 8 Open stockyard system layout ... 18

Figure 9 Flow diagram of open stockyard system ... 19

Figure 10 Closed stockyard system - layout 1 ... 20

Figure 11 Flow diagram - Closed stockyard system Layout 1 . ... 20

Figure 12 Closed stockyard system - layout 2 ... 21

Figure 13 Flow diagram - Closed stockyard system - layout 2 . ... 21

Figure 14 Eurosilo - stacking mode ... 29

(8)

vi

Figure 16 Cost recovery period of higher installation costs of closed stockyard system ... 39

Figure 17 Cost recovery period vs % of coal losses... 40

List of Tables

Table 1 Comparison between layouts of closed stockyard system ... 22

Table 2 Brief specifications of conveyors in open stockayrd system ... 24

Table 3 Brief specifications of open stockyard equipments ... 25

Table 4 Brief specifications of the conveyors in enclosed stockyard system ... 28

Table 5 Brief specifications of Eurosilo equipments ... 29

Table 6 Comparison of Open and Closed stockyard (Eurosilo) systems from technical and operational view points ... 37

(9)

1

1. Introduction

In the event of recent changes in environmental norms in India, India’s biggest power producer, National Thermal Power Corporation (NTPC) has been facing heat regarding the pollution created by its coal based power plants (Centre for Science and Environment, 2015). The reasons for the pollution, majorly, are the exhaust from the power plant and the dust from the large coal stockpiles. Even though poor coal quality (PTI, 2014) is the main reason for such pollutions, questions have been raised by various concerned environmental agencies regarding the credibility of the technology used by NTPC’s power plants.

Another pressing issue faced by NTPC is the land availability. To meet up with NTPC’s target of 800 GW power by 2030 (Sinha, 2015), numerous new power plants or expansions of existing power plants have been planned. For the new power plants, securing adequate empty land is a problem while for expansion of power plants, available land is inadequate for augmenting the system (SAIKIA, 2013). In the wake of rising land prices and the surrounding areas being inhabited by people, complying with environmental norms and constructing the power plant with less foot print has become prime importance. The Eurosilo system (closed storage) has been gaining wide popularity in the world market for its use in coal storage. Hence a feasibility study is being conducted comparing the closed storage system with the conventional open storage system used in India for a specific case scenario.

The purpose of this report is to showcase the feasibility of the closed storage systems on the basis of Environmental Management Accounting (EMA) (United Nations Division for Sustainable Development, 2001) (Schott, 2007). EMA compares the initial costs, annual costs and the end of life costs and enables to make a comprehensive analysis on the life cycle cost of the systems. The analysis is done by making a conceptual design of the systems, drawing the basic specifications and arriving at the costs of the system. The first step is formulating the design criteria based on the coal requirement of the power plant and other statutory design requirements. Delft systems approach (Hans P.M. Veeke, 2008) is followed to perform a methodical approach to the selection of the system design for both open and closed storage systems. This approach is explained in Chapter – 2. Once the system design of the open and closed storage systems are fixed, the basic specifications of the open and closed storage systems are formulated to satisfy the design criteria and the delft systems methods, which is detailed in Chapter – 3&4. The report will answer the following questions:

1. What are the best configurations of open and closed storage systems for the power plant case?

2. As per EMA, what is the best solution for storage system in the power plant?

Chapter – 5 enumerates the evaluation of the open and closed storage systems based on EMA. The cost heads are fixed based on the guidelines of the UNEP and the costs are obtained to perform the evaluation. The evaluation of the system based on a technical and operational view point is also presented. Finally Chapter – 6 gives the conclusions as a result of the evaluation based on EMA and further recommendations for the comparison based on EMA.

(10)

2

2. Approach to the design process

The feasibility study is being conducted to compare the choice of closed and open storage systems and both the systems should be designed to satisfy the same requirements. These requirements are translated as the design criteria, which forms the basis of the design. A conceptual design of the open and closed storage systems are made and for such a conceptual design, the Delft Systems Approach is followed, which is explained in detail in this chapter.

2.1 Design Criteria

The design criteria are the explicit standard requirements the system needs to satisfy. They could be distinguished as primary and secondary, where primary design criteria are to be satisfied by the system design necessarily whereas the secondary design criteria are those features that are highly desirable but not essential.

2.1.1 Formulation of the design criteria

The design criteria of the open and closed storage system for this feasibility study would be set to satisfy the requirements of the power plant. The storage system should be designed such that it is able to supply the power plant boilers, whenever they are operated, with coal at a desired rate. The design criteria vary with the capacity of the power plant, site conditions, and quality of coal. The formulation of design criteria mainly depend on the operation of the power plant and the owner’s experience with the power plant equipment and coal handling equipment in the past. In order to avoid using widely varying practices and to establish uniformity in the approach to the design of power plants, Central Electrical Authority (CEA) issued a design guideline/ standard design criteria (Central Electricity Authority, 2010) based on which the power plants of capacity more than 500 MW could be designed. The design criteria for the coal handling plant have been formulated based on the guideline.

The reference case chosen for this feasibility study is a power plant of capacity 2 x 660 MW. The coal storage is supposed to meet the power plant’s requirement for 20 days. The storage capacity is decided based on the storage requirement, gross calorific value of the coal and the heat rate of the boilers. This design criteria applies to the entire coal handling system of the power plant.

The capacity of the conveying systems, however, is based on meeting the peak coal requirement at the boiler considering only 12 hours of operation for coal handling system. The 10% margin is added on top of the rated capacity to arrive at the design capacity of the coal handling conveyors.

Powerplant capacity 2 x 660 MW

Coal Storage 20 days

GCV(avg) 3400 kCal/kg

Heat rate 2317.44 kCal/kW

(11)

3

SCC 0.682

Daily coal req 21593.088 Tons

Hourly Coal req 899.712 TPH

Peak coal req 1022.4 TPH

Considering 12 hours 2044.8 TPH

10% margin 204.48 TPH

Rated capacity 2249.28 TPH

Rounded off 2250 TPH

Design capacity 2475 TPH

The stockyard capacity should be able to satisfy the daily coal requirement of the boiler for the expected number of days (20). In case of a blended coal fed to the boiler, the stockyard should be calculated to have both indigenous and imported coal. On meeting with NTPC, it was indicated that the boiler would be operated with coal having either 100% indigenous coal, or blend of 70/30 capacity of indigenous/imported coal. Based on this, the indigenous coal quantity should be enough to satisfy the operation with 100% indigenous coal capacity for 20 days and the imported coal stockpile quantity should be able to satisfy the operation with 30% coal capacity for 20 days. It was also learnt that it is a practice to store the indigenous and the imported coal separately in the open stockpiles.

Hence the coal stockyard capacity would be:

Amount of reserve for Indigenous coal 431862 Tons

Amount of reserve for Imported coal 129600 Tons

2.1.2 Other statutory design requirements

The design guideline issued by the Central Electrical Authority is only pertaining to open storage system because the closed storage concept is not a popular one in India yet. Hence the other statutory design requirements are related to the open stockyard system. They are as follows:

1. There shall be two streams of conveyors interlinked at transfer points for conveyor changeover for flexibility of operation. The stockyard conveyors should be reversible to facilitate stacking and reclaiming of coal through the same conveyor belt.

2. All the mechanical, civil and electrical components of the system should be designed considering the plants operate round the clock every day and both conveyors are run simultaneously at the rated capacity.

3. The motors, gearboxes, couplings and pulleys for conveyors shall be standardized and limited to a minimum as much as possible.

4. For stacker reclaimer,

a. The wheel load of the stacker reclaimer shall not exceed 27 tonnes. b. The ratio of the boom length and the track gauge shall not exceed 5. c. The minimum track gauge width shall be 7 m.

d. Maximum coal stockpile height shall be 10 m.

e. Buckets shall be designed for 125% of the rated capacity. Rate of the bucket discharges shall not exceed 55 per minute.

(12)

4

5. Slope of the conveyors shall be zero at the feeding point as much as possible and the angle of inclination shall not be beyond 16 degrees.

Only those mentioned in the design guideline are mentioned here, there might be a few extra design requirements based on the location and customer of the plant. For the closed storage system, the same design criteria applies, however there are no standard design requirement on the design and operation of the equipments inside the Eurosilo system.

2.2 Delft systems approach

The next step in the feasibility study is to develop the design of the two systems – open and closed storage to suit the design criteria and standard requirements of the customer. Since it is a feasibility study, only a conceptual design is made, which would be able to give a good perspective on the costs involved for employing both systems. The Delft Systems approach provides a very simple yet comprehensive method, incorporating various aspects for approaching a design process. For creating a design, a structured approach is followed by the application of PROPER model and innovation model. The basics of the models and its elaboration for application are not introduced in this chapter’s section. The reader is encouraged to refer the book “The Delft Systems Approach – Analysis and Design of Industrial systems” to get familiar with the terminologies, models and the procedure, which is applicable for all industrial systems. The procedure depicted in the book has been followed and how it has been adapted to develop a conceptual design for the feasibility study in a structured manner is explained in the subsequent chapters.

2.2.1 Defining the system, functions

The first step in any design process is first to understand the system and the function to be fulfilled. The system is a defined as a collection of interacting elements which could be grouped together as sub systems, satisfying various sub-functions. The system in consideration is a stockyard system which performs a function inside an environment (the power plant). It has an input from its environment and an output that needs to be delivered after a series of activities, satisfying some predetermined requirements/constraints.

The primary functions of a stockyard are (ThyssenKrupp Industrial Solutions, 2014):

a. Serve as material buffers, reserve or blending between mining, processing and transshipping.

b. Balance out fluctuations in the quantity and quality of raw materials.

In a stockyard system, there are sub-functions such as stacking, reclaiming and blending which are achieved by a group of interacting elements (subsystems) in the stockyard system.

2.2.2 Function design and process design - introduction

The approach to the design of a system is considered to be a combination of the design of the product (the system itself) and the design of the process (the way in which the industrial system works). The former is termed as function (or product) design and while the latter is termed as

(13)

5

process design. The design process in 2 parts, based on an application of PROPER model via innovation model, is depicted in the figure below in comparison with the 3 steps described by Jonas.

Figure 1 Innovation model as a design process (Hans P.M. Veeke, 2008, p. 184)

As evident from the picture, the function design is determining the intended results, what are the ways to achieve them and the starting point of the process design is determining what can be required from the system. To sum it up, the function design gives us the system configuration, system boundary and what the system should achieve, while the process design is a multi-disciplinary approach to determine the structure of the system i.e the way the elements interact with each other in order to achieve the goals. The process design approach takes into account all the disciplines involved in the system within the system boundary chosen during function design. The connection between the function design and the process design is depicted in the figure below. The figures 1 and 2 show the basic structure of the approach followed to design the stockyard system. More details in each step of the design are elaborated in the following chapters.

(14)

6

2.2.3 Function design approach

The steps in the function design (Hans P.M. Veeke, 2008, pp. 185-188) are explained by the functional terms of the innovation model. This is achieved with iterations to explore the possibility of achieving the intended results with a variety of available solutions and to end up with a feasible and desirable system configuration.

Step 1 – Explore the environment and determine the objective

The environment is where the system belongs. For the stockyard system the environment is the power plant. Exploring the environment will give the needs of the environment. This need is translated into objectives, preconditions and principles.

Objectives are the results the system is supposed to deliver and are expressed in terms of the PROPER model.

 Order flow: What is the demand composed of, what is the required lead time and what is

the required reliability of the delivery?

o In case of the stockyard system, the demand is the quantity of coal based on the daily requirement at the boiler, the lead time is the operating hours of the system which is 12 hours and the required reliability of the delivery is the conveying capacity rate to satisfy the boiler requirement within the lead time.

 Product flow: what are the products required, what is the required quality and quality and

what are the costs and flow times.

o The products required are nothing but coal with an average capacity to satisfy the boilers requirements. The quality of coal is determined by the Gross calorific value of the coal that is fed to the boiler to achieve the required power production. The costs for the product as objective is usually unlimited, however a budget is drafted by the customer.

 Resource flow: what is the required quality and quantity of resources with respect to the order and product flows.

o The resources are the equipments used, the number of equipment are determined by the standard industrial practices with respect to the limitations of the powerplant in terms of location of the powerplant, area available and the climatic conditions. The quality of the resources is determined by the industrial quality requirement standards in terms of design, fabrication, installation, maintenance etc. which are determined by the customer or governing authority or both.

 In terms of establishing the relationship between the flows, questions are:

o Between order and product flow: what is the ratio of the order quantity to product quantity. The answer is 1 because the coal requirement at the boiler needs to be satisfied by output of the stockyard system at full capacity always.

o Between the resource and the product flows: what is the required flexibility of utilization. For design purposes, the utilization rate is usually considered to be 100%. Preconditions are nothing but statutory regulations, environmental laws, which fall outside the range of influence of the system and dictate the way the design proceeds. In this case there are

(15)

7

no explicit environmental laws for the stockyard system. However, the dust emission norms of the powerplant, which is the environment for the stockyard system, is considered to be the precondition.

Principles are usually based on the company’s culture. In this case, that would be storage of indigenous and imported coal in separate stockyards and not in the same stockyard with different layers. The system should be 100% redundant to enable running the system even in case of an equipment failure. In this specific case, using the minimum land area possible is another objective for this system, which could be seen as a principle of the power plant owner.

Step 2: Define alternatives

In this step, the possible alternative configurations to satisfy the objectives are formed. Its an iterative process to determine the context, function, structure and behaviour.

 Context determination: Context determination is nothing but determining the system

boundary. The system, the stockyard, is considered to be a part of a larger chain. The systems inputs are considered as the coal that is fed into the stockyard system from the trains via wagon tippler complex (Wagon tippler, side arm charger, bunkers. Paddle feeders) or long distance conveyors. The stockyard has a function to store the coal and the output is the required quantity of coal fed to the day bunkers or directly fed to the mills, with desired quality.

 Function determination: The primary function is divided into sub-functions. The intended

result is defined for each sub function. The primary function is to store the material (coal) and provide the necessary quantity of coal in desired quality for the operation of the powerplant. This main function could be divided to involve the following subfunctions – transfer, transport, stack, reclaim and blend.

The schematic below provides a representation of the context and the function, subfunctions of the stockyard system.

Figure 3 Context determination - Stockyard system

 Structure determination: This step involves rearranging and grouping the subfunctions in

different ways to obtain different structures which would achieve the intended results. This grouping could be done in any way, horizontally or vertically. The two ways of determining a structure would be combining or splitting either flows or functions.

(16)

8

In this feasibility study, the structure concepts needs to be developed for both open stockyard and closed stockyard systems. The following figures 4 & 5, depict the available equipment to satisfy the primary function and subfunctions. Combination of the equipments would result in various possible system configurations or alternatives.

 Behaviour determination: Each structure generated for the open and closed stockyard

system causes a behaviour. The behaviour of each structure concept influences the results and the efforts needed to achieve the results. This behaviour is either seen as the communication requirements between the elements of the structure or the time dependent behaviour interms of stocks of material that could be stored, throughput time of each element/ structure as a whole etc. Therefore each structure exhibits its own specific behaviour.

(17)

9

(18)

10

(19)

11

Step 3: Confront and tune:

The steps 1 and 2 provide the intended results and the results that could be expected in case each alternative configuration is chosen. The step 3 determines the efforts that are expected for each configuration. The discipline involved in every industrial system is identified as technology, organization and information. Confrontation step is basically identifying the questions that need to be answered to make sure a system is feasible, desirable and reliable. This also involves costs. The following could be the questions that need to be answered for each alternative in case of the open and closed stockyard systems.

Technology:

1. Are the functions technologically achievable (feasible)? 2. What kinds of equipment are required?

3. What are the consequences with respect to operations, maintenance and environment? Organization:

1. What are the system configuration aspects in the system?

2. Are the objectives achieved without disturbing the environment (complete material handling system)?

3. What are the demands on the competencies of people and other resources? Where can they be obtained? What are the training and operational efforts required?

Information:

1. What are the demands on the architecture, software and hardware?

2. Which administrative systems, control systems and products are required?

This primary objective of this step is the reason for conducting the feasibility study. The results of the feasibility study shall be inline to answer the above questions coupled with the result of EMA which would be described in detail later.

2.2.4 Choice of stockyard system configuration based on design criteria.

The design criteria, as a result of function design, is once again summarized here. The quantity of the coal to be stored, the rate at which the coal has to be fed to the boilers, the gross calorific value of the coal fed into the boilers answer the order flow and the product flow of the product design. The resource to be used, the machines are designed as per the prevailing Indian standards. Apart from these criteria, the following points have to be kept in mind:

1. The dust emission from the stockyard system should not exceed 30 mg/m3. 2. The conveying system should have 100% redundancy for reliability and flexibility. 3. The area used for the installation of the entire system should be minimal.

Powerplant capacity 2 x 660 MW

(20)

12

GCV(avg) 3400 kCal/kg

Heat rate 2317.44 kCal/kW

Plant life 30 years

SCC 0.682

Daily coal req 21593.088 Tons

Hourly Coal req 899.712 TPH

Peak coal req 1022.4 TPH

Considering 12 hours 2044.8 TPH

10% margin 204.48 TPH

Rated capacity 2249.28 TPH

Rounded off 2250 TPH

Amount of reserve for Indigenous coal 431862 Tons

Amount of reserve for Imported coal 129600 Tons

The available solutions for all functions and subfunctions have been listed in the figures 4 & 5 with respect to the open and closed stockyard systems. The best stockyard configuration for both scenarios will be chosen based on the design criteria.

Stockyard system configuration for open stockyard system

a. Primary function – Storage

The open stockyard system could be made in the different forms such as conical, radial and longitudinal trapezoidal stockpiles, to store the required coal quantity as shown in the figure. If the required quantity is considered to be stored in 4 stockpiles of 140,000 tons capacity each, the required conical diameter for one stockpile would be 120 m with a height of 43.5 m approximately. The radial stockpile would be running for a higher diameter with more land area.

The design requirement for the stockyard height is 10 m, which has been decided after long years of experience in operating coal stockyards. This height restriction has been established to reduce the effect of wind blowing on the stockpile thereby minimize dust emissions and the effect of oxidation due to wind. Hence the conical pile and radial stockpile are not considered. Whereas the longitudinal stockpile with trapezoidal or triangular cross section, which could be created at a height of 10 m with the minimum area is considered.

b. Transport

The options available for transportation of coal from one place to another are dumper trucks and conveyors. For a daily requirement of 21593 tons of coal at the bunker, atleast 10 trucks and 20 payloaders are required to be running around to satisfy the demand for 12 hours of operation. Also dumper trucks are discontinuous transport method and the utilization rate of the trucks would be 50% only since they run empty most of the time. This is not desirable. Hence conveyors are considered.

(21)

13

c. Transfer

The function of transition of coal from one equipment to another is called transfer. This could be facilitated by different equipments like hopper, chute and tripper car between transport equipment and the equipment that performs the next function “stacking/transport”. The hopper is used only when there is a difference between the discharge rate of the equipments between which the transfer takes place. Hence hopper is not used. For a transfer between conveyor to conveyor, a chute is preferable and for transfer between the conveyor and the stacking machine, a tripper is used.

d. Stacking

Stacking is nothing but creating pile of material (coal). This could be achieved by different machines ike conveyor, radial stacker, screw augers, long boom slewing stacker, rail mounted non-slewing or slewing stacker and Bucket wheel stacker cum reclaimer

Conveyor, radial stacker, screw augers and long boom slewing stackers cannot stack the coal in a longitudinal fashion. The best choices for stacking coal in the chosen storage configuration are rail mounted non-slewing or slewing stacker and Bucket wheel stacker cum reclaimer

e. Reclaiming

Reclaiming is when the coal that is stacked is retrieved from the stockpile. This could be achieved by a combination of payloaders+trucks, screw auger, scraper reclaimer(portal/semi-portal/bridge type), drum/barrel reclaimer and Bucket wheel stacker reclaimer.

Payloaders+ trucks combination is not desirable because that would create a huge number of vehicles employed and higher lead time in reclaiming. The screw auger acting over a free surface of bulk solid has limited reclaiming capacity only and is not suitable with the longitudinal stockpile configuration. The scraper reclaimer and the drum/barrel reclaimers are also used for applications with lower discharge rate. Also use of scraper reclaimer and drum/barrel reclaimer for reclaiming operation means scraper rail mounted non-slewing or slewing stacker is used. The bucket wheel stacker cum reclaimer incorporates both stacking function with the help of a boom conveyor and the reclaiming operation with the help of the Bucket wheel at the end of the boom conveyor. Only one machine per stockpile is sufficient for stacking and reclaiming operation. Hence this equipment is the most preferable for stacking and reclaiming operation.

f. Blending

Blending is the integration of different raw materials with different characteristic to produce a mixture of a desired specification or blend. It could be done by either discharging coal from different silos at the required percentage of constituents onto a same conveyor or reclaim coal at different discharge rates from stockpiles of different coal qualities and blend them on the same conveyor. It could also be done by storing the different types of coal in layers in a stockpile and create a blend when the coal is reclaimed using a reclaiming machine.

(22)

14

It has been specified that the different qualities of coal have to be stored in different stockpiles. Hence the preferred option is reclaiming from stockpile using the reclaiming machine and depositing on to a conveyor to create a blend.

g. Dust control

Dust control at an open stockyard is a challenge and the dust emissions as per new emission standards should not exceed 30 mg/m3. The most used and widespread solutions are use of cellulose crust, tarpaulin and water sprinklers on the stockyard.

The cellulose crust could be used to cover the coal stockpiles thereby forming a blanket which will prevent the coal dust being liberated into the atmosphere due to strong winds. However, the major disadvantage is that in an open stockyard due to rain the cellulose crust dissolves and is ineffective in rainy seasons/with wet coal. Tarpaulin is not a feasible solution since a huge area of stockpile needs to be covered and it is not easy to use. Water sprinklers installed along the length of the stockyard spraying water on the stockpiles when the coal is stacked and reclaimed could be a feasible option. This method is feasible and the most prevalent method for dust suppression in open stockpiles. The chosen system configuration is depicted in figure 6.

Stockyard system configuration for closed stockyard system

a. Primary function – Storage

The closed stockyard system could be made in the different forms such as covered storage with longitudinal trapezoidal stockpiles, circular dome storage and mammoth silos(Eurosilo) to store the required coal quantity as shown in the figure 7. The height restriction, as a part of design requirement for the stockyard is not considered since this is a closed system. All 3 solutions are feasible and effective, however the longitudinal covered stockpile (6410 m2 approx) and the circular dome storage(4750 m2 approx) occupy more surface area than the mammoth silos(2400 m2 approx).

Also the use of mammoth silos removes the necessity for a dust control system which would be required in case of the longitudinal covered stockpile and the circular dome storage. Hence the mammoth silo is the preferred option for storage.

b. Transport

As mentioned in the choice of transport for open storage, conveyor is preferred.

c. Transfer

As mentioned in the choice of transfer equipment, hopper, chute and tripper are viable options. However in the mammoth silo option the transfer is made between conveyors, hence only chute is preferred.

(23)

15

d. Stacking

Stacking in closed storage could be achieved by different machines like, screw augers, long boom slewing stacker, rail mounted non-slewing or slewing stacker and Bucket wheel stacker cum reclaimer

However inside the mammoth silo the most preferred option is screw augers which could be used for both stacking and reclaiming by switching the direction of rotation.

e. Reclaiming

As mentioned above, the screw auger is preferred for reclaiming.

f. Blending

Conveyor running underground beneath the silos containing coal of different qualities is the preferred and effective method to create a desired blend since the rate of discharge could be easily controlled and a blend is formed.

g. Dust control

Since the mammoth silo is used, there is no need for dust control systems. The chosen system configuration is depicted in figure 7.

Thus the system configuration of open stockyard system and closed stockyard system has been figured out.

2.2.5 Process design approach

Process design starts when the configuration is selected. For this feasibility study, based on the function design, system configurations for open and closed stockyard systems have been chosen. These system configurations will be developed further and compared in the process design. The development of the system configuration will involve determining the interaction of the equipments in the system and performing the same methodology in all disciplines of the system namely technology, organization and information. Only the technological process design will be focused for this feasibility study, and for the other disciplines, process design would be theoretically suggested and compared when analyzing the feasibility of both open and closed stockyard systems.

Technological design process mainly focuses on the resource flow of the system i.e the design of machines, tools and transportation equipment. Function groupings that were established during the function design shall be physically filled at this stage.

(24)

16

(25)

17

(26)

18 Following are the steps:

1. Establishing needs and generating ideas. – which results in requirement

specifications(functional, design requirements and design criteria). This has already been addressed in the function design section 2.2.3

2. Conceptual Design – Decision making performed to obtain a concept. This is a very

important step because the design changes are still cheap to implement. The conceptual design results in the preliminary combination of the element interactions in the system.

3. Preliminary or detailed design – Layout and form are quantified during this step. The basic

specifications of the system and the equipments of the open and closed stockyard system are obtained as a result of the system.

4. Final design – Detailed analyses are performed. 5. Implementation.

In the feasibility study, only steps 1,2 and 3 of the process design is performed. The result of the process design will give the basic specifications of the open and closed stockyard system to be evaluated and compared.

2.2.6 Conceptual system design of the open stockyard system

The system boundary as defined during the function design states that the boundary starts after the transfer of coal from the crusher and it ends with the reclaim conveyor from the stockyard. The system design of the stockyard is fairly simple and the configuration depends on the land available within the layout of the whole power plant. The open stockyard system layout for the reference case has been depicted in figure8. This system has been designed to incorporate the system configuration as determined in the function design to satisfy both the primary and secondary design criteria. The flow of coal within the system is also represented in a flow diagram (figure 9).

(27)

19

Main features:

The scope starts from the point where the crushed coal is transferred to the stockyard conveyor and ends at the point where the stockyard conveyors transfer the coal to the infeed conveyors of the boiler bunker. To make the system flexible and to satisfy the requirement of redundancy, the transfer points viz, the crusher house, reclaim hopper house and the transfer point-1 are equipped with flap gates(for transfer from one conveyor to either of two conveyors) and a series of flap gates (for transfer from one conveyor to one of three conveyors).

The stockyard conveyors pertaining to the stacker reclaimers are reversible, to enable the stacking and reclaiming by the same conveyor, while the stockyard conveyor pertaining to the bucket wheel reclaimer is uni-directional. This also enables the bypass of the coal from the crusher to the boiler bunker via TP-1.

Figure 9 Flow diagram of open stockyard system

2.2.7 Conceptual system design of the closed stockyard system

In case a closed stockyard system is to be installed inside the same layout of the power plant instead of an open stockyard system, multiple options could be come up with within the available land area. The following are a few layout options as depicted in the figures below.

(28)

20

Layout 1:

Figure 10 Closed stockyard system - layout 1

In this layout, the silos have been arranged in two rows and the coal after getting crushed at the crusher house is fed to the silos by two different streams of conveyors. The 3 silos in line are used to store the indigenous coal and the two silos in line are used to store the imported coal. The conveyors BC 11 A/B and BC-12 A/B are envisaged on top of the coal silos to feed them with the help of mobile trippers. There are reclaim conveyors (BC-13,14, and 15) under every set of silos which would convey the coal in proportionate amounts for the blend onto BC-2A/B for blending. The flow diagram is indicated in the figure below.

(29)

21

Layout 2:

Figure 12 Closed stockyard system - layout 2

In this layout, all the silos have been arranged in line. The coal from the crusher house is conveyed to the silos by a series of conveyors. The BC-10A/B rises up to the height of the coal silo and then transfers the coal to BC-11 A/B which feeds the coal to a reversible conveyor RBC-1A/B. This reversible conveyor enables feeding the silos on either side of itself. The silos 1A, 1B, 1C are used to store indigenous coal while the silos 2A and 2B are used to store the imported coal. Operation of the screw augers from any 2 indigenous coal silo and 1 imported coal silo will enable to achieve the required capacity and the required blend on the reclaim conveyor. The reclaim conveyor BC-15 A/B transfers the blended coal from the silos to the transfer point 1 which will feed the succeeding conveyors into the bunker boiler. The flow diagram is indicated below.

(30)

22

A comparison of the above two layouts have been described in the table below.

S. No

Description Layout 2 Layout 1

1 Total length of conveyors Approx 1.85 kms (2A/B,

10A/B, 11A/B, 12A/B, BC-13A/B, BC-14A/B, BC-15A/B & RBC-1A/B)

Approx 3 kms (BC-2A/B, BC-10A/B, BC-11A/B, BC-12A/B, BC-13, BC-14, BC-15)

2 No. conveyors operating

during reclaiming mode

Only one conveyor (BC 15 A or BC 15B) is operated for reclaiming.

We understand atleast 2 (maybe all 3?) conveyors out of conv BC-13, BC-14, BC-15 will be operated during reclaiming mode to achieve reclaiming capacity since reclaiming rate from a single silo is limited.

3 Transfer points TP-1 and 2 no. of transfer points

for silos.

TP-10, TP-11, TP-1, TP-2 and 2 no. of transfer points for silos.

4 Land area required 400x 100 sqm approx. 400x230 sq m approx.

5 Redundancy requirement

satisfied

Yes Yes

6 Consumed power Lesser consumed power since

only lesser number and relevant conveyors are operated at any time

Consumed power is higher when compared to Layout -1 because all the mobile trippers and the infeed conveyors need to be operated for stacking mode.

7 Infeed conveyor system at top

of silo

Combination of reversible conveyors and individual uni-directional conveyors are considered. The conveyors could be designed to have standardized components.

6 no.s Mobile trippers are considered which might increase the load on the roof structure of the silo

8 Conveyors in an elevated state Approximately 350 m of

conveyor require trestles. Hence structural steel quantity for support would be lesser compared to Layout 1.

Approximately 600 m of conveyor length requires trestle support.

Table 1 Comparison between layouts of closed stockyard system

From the table 1, it is evident that the layout 2 has lesser length of conveyors, lesser footprint and lesser consumed power when compared with layout 1. Hence layout 2 is chosen.

(31)

23

3. Preliminary design of the open stockyard system

The details of the open stockyard system, which is the conventional design for all the power plants in India, have been explained in this chapter. The scope of the open stockyard system, the layout and flow diagram has been already discussed in the section 2.2.6.

3.1 Function – Storage

The storage of the coal, in case of an open stockyard system, is achieved by stacking the coal inlayers in a longitudinal fashion, to obtain a stockpile in a trapezoidal cross section. As mentioned in the subsection 2.1.2, the height of the stockyard cannot be more than 10 m and the minimum track gauge is supposed to be 7 m. It is also mentioned that the boom length of the stacker reclaimer, which is measured from the centre line of the slew to the centre line of the bucket wheel, shall be not be greater than 5 times the length of the track gauge. This means that the minimum allowable length of the boom shall be 35 m approximately.

The width of the stockpile shall be such that the boom length of the stacker reclaimer is able to cover the entire width of the stockpile for stacking and reclaiming purposes. Considering the angle of repose of the coal to be 37 deg, the stockpile shall be approximately 46 m (considering atleast a 8 m dia bucket wheel) in width for an efficient stacking and reclaiming operation. In the current design, totally 3 stockpiles of 140,000 tons for indigenous coal and 1 stockpile of 140,000 tons capacity for imported coal has been envisaged.

The dimensions of the stockpile are as follows.

Dimensions of stockyard

For stockpiles of size 140000 tons

Volume of one stockpile 164750 m3 of material

Height of the stockpile 10 m

Top face of the stockpile 12 m

Angle of repose of coal 37 deg

To find Length of the stockpile

Width of pile due to slope 13.33 m

Total width of pile 46.5 m

Length of the pile 707 m

3.2 Function – transport

The coal is transferred from the crusher to the designated stockpiles by means of conveyors. The conveyors BC-2A/B between the crusher house and the Transfer tower TP-1 receives the coal from the crushers and acts as either a by-pass to send the coal to the boiler bunker or transfer the coal to stockyard conveyor BC-7B for stacking.

(32)

24

The stockyard conveyors BC-7A/B are reversible conveyors operating over the trippers for stacker reclaimers while the stockyard conveyor BC-7C is used as a reclaim conveyor to convey the coal reclaimed by the bucket wheel reclaimer to the conveyors BC-2A/B at reclaim hopper house RH-1. The brief specifications of the conveyors are given below.

S.no Conveyor Length (m) Absorbed

power(kW) Motor Power (kW) 1. BC – 7A 765 328 375 2. BC – 7B 765 328 375 3. BC –7C 765 207.58 225 4. BC – 2 A/B 155 183.84 235

Table 2 Brief specifications of conveyors in open stockayrd system

3.3 Function – stacking

The stacking of the coal is done by rail mounted bucket wheel stacker reclaimer which as the name implies, is capable of both stacking and reclaiming the coal. The stacker reclaimer consists of a travelling mechanism on which there is a slewing base. The boom is attached to this slewing base which has a conveyor to stack the coal and transport the reclaimed coal to the reclaim conveyor. The boom conveyor of the stacker reclaimer is a reversible conveyor. At the end of the boom, is a bucket wheel which has buckets at the periphery to cut into the layers of coal from the stockpile. The stacker reclaimer can slew to any position in order to stack and reclaim the coal. Above the slewing base is the mast structure to which the boom is attached by means of tie rods near the bucket wheel end and via hydraulic cylinders for luffing near the drive end of the boom conveyor.

The boom conveyor can be moved up and down (luffing operation) by activating the hydraulic cylinders to enable stacking and reclaiming at different levels of the stockpile. Horizontally opposite to the boom conveyor is a counter weight hinged to the mast structure which balances the loads due to stacking and reclaiming of the coal and keeps the machine stable during all modes of operation. In the stacker reclaimer, there is a provision to have the stockyard conveyor be used for both stacking and reclaiming purposes. The stockyard conveyor passes over an elevator and a tripper conveyor to feed the stacker reclaimer. The elevator is provided with a cylinder which, in an expanded position, keeps the elevator in an inclined position to feed the tripper. When the cylinder is retracted, the elevator is flat, enabling the conveyor to be operated in a reverse direction.

The stacker reclaimer is equipped with belt weigh scales to measure the quantity of material stacked and reclaimed, pull cord switches, belt sway switches and other control devices for safe and reliable operation of the stacker reclaimer. At the end of the rails(either end of the stockyard), there are storm anchoring positions envisaged, so in case of storm, the stacker reclaimer could travel to the anchoring position and tied down by special anchoring devices for safety.

3.4 Function – reclaiming

Reclaiming can be done by both stacker reclaimer and reclaimer. The reclaimer is similar in construction to the stacker reclaimer, except that there is no tripper structure that transfers the material from the stockyard conveyor to the machine. The bucket wheel at the end of the boom is fitted with buckets having teeth to cut into the coal stock pile. The bucket wheel is mounted on a bearing pedestal and is driven by a hydraulic/electrical drive.

(33)

25

When the bucket wheel is operated, the buckets dig into the coal surface and transfer the coal on the boom conveyor which conveys the coal to the stockyard conveyor. In case of an open stockyard system, to facilitate stacking and reclaiming at the same time, one reclaimer is envisaged to reclaim coal from 2 stockpiles in addition to the 2 stacker cum reclaimers.

S. No Description Bucket Wheel Stacker

Reclaimer

Bucket wheel

Reclaimer

1 Quantity 2 1

2 Stacking rate 2250 TPH(Rated)/ 2475 TPH

(Design)

-

3 Reclaiming rate 2250 TPH(Rated)/ 2475 TPH

(Design)

2250 TPH(Rated)/ 2475 TPH (Design)

4 Stockpile height 10 m 10 m

5 Stockpile width 46.5 m 46.5 m

6 Travel Speed 0 – 20 m/min 0 – 20 m/min

7 Track gauge 10 m 10 m

8 Boom length 42 m 42 m

9 Boom Conveyor belt width and

speed

1600 mm 1600 mm

Table 3 Brief specifications of open stockyard equipments

3.5 Function – blending

The blending operation in an open stockyard is done at the conveyors BC-3A/B at the transfer point-1 where the low calorific value and high calorific value coals will be transferred from different stockyards on to the same conveyor. The reclaim rate for the imported coal, when compared to the reclaim rate of the indigenous coal, is of the same proportions to the percentage of the imported coal required in the blend. The reclaim rate of the imported coal can be adjusted by adjusting the rotation speed of the bucket wheels, thereby obtaining the required blend.

3.6 Other functions

Depending on the sophistication required by the customer in the operation of the stockyard, the machines could be manned or unmanned. However, some features are mandatory and necessary for the open stockyard system in order for it to be efficient and reliable on a long term. Dust control throughout the stockyard system, fuel management system to keep track of the inflow of coal and coal usage in the powerplant.

3.6.1 Dust control

The main problem with open stockyard is the spontaneous combustion and the dust generation due to the local wind conditions. Even though the height of the stockyard is stipulated to be 10 m at the maximum, it is highly recommended to install dust control system to eradicate the dust generation from the stockyard. Dust is generated at the stockyard during the following occasions:

1. when the coal is transferred from the tripper to the boom conveyor 2. when the coal is stacked on the stockpile by the boom conveyor

3. when the coal is dug from the stockpile by the bucket wheel and transferred on to the boom conveyor for reclaiming.

(34)

26 4. when the wind blows on the stockpiles.

Dust is also generated at the transfer points when the coal is transferred from one conveyor to another. There is a dry fog dust suppression system or a dust extraction system envisaged at these transfer points depending on the customer’s specification. However, in the system considered, Dry fog dust suppression system has been considered at the points where the coal is transferred from one conveyor to another, for example conveyor crusher house, reclaim hopper house and transfer point (TP-1). Dry fog dust suppression system is also considered on the machines at the transfer points referred above(points 1,2 and 3) and is designed to be operated in a stand-alone mode. To prevent dust generation due to wind, the stockpiles are sprayed on with water by a separate system all along the length of the stockpile. This stockyard dust suppression system consists of sprinkler installed at intervals of 30 m on either side of the stockpile connected to each other with pressurized water running along the piping network. The transfer points are all envisaged with service water, potable water and drainage water systems.

3.6.2 Fuel Management system

The main objective of the fuel management system is to control and keep track of the coal flowing into the system. This would entail keeping record of the coal source and properties of coal, routing the coal to the appropriate stockpile by means of conveyors, keeping track of the volume of coal flowing and being stored in the system at the respective stockpiles, controlling the blend of the coal by regulating the operation of the related conveyor, stacker reclaimers etc. These could be done fully automatic fashion but conventionally, these are done semi-automatic with human involvement in operating the stacker reclaimer machines and monitoring at the PLC/ plant control room.

The records of the type and source of the coal are fed into the system, the amount of coal flowing via the conveyors is kept track by means of belt weigh scales installed on the conveyors at strategic points. Belt weigh scales are also installed on the stacker reclaimer booms to monitor is the reclamation operation is performed inline with the command/requirements from the main control room. The belt weigh scales provide the feedback about the status of the coal flowing at different points in the system which would enable the operator to make decisions on adjusting the coal flow. This management system will also help the plant operator to audit the performance of the system.

(35)

27

4. Conceptual design of closed stockyard system.

In this chapter, the closed stockyard system design with Eurosilos is elaborated. As mentioned previously, this system is chosen to be the best amongst the alternative system designs that were formed. The chosen system design satisfies all the design criteria and other requirements of the customer. The preliminary design should be performed in line with the standards acceptable to the power plant customer/users.

4.1 Function – Storage

The storage sub-function is achieved by a mammoth silo (Eurosilo), with a circular cross section and stores the coal in layers upto a certain height within itself. The large storage capacities, yet minimum foot print, of Eurosilo is attributed to the feature that coal is stacked in a vertical manner. For

achieving the storage, 3 silos of 100,000 m3 capacity for the indigenous coal, and 2 silos of 100,000

m3 for the imported coal is considered. The following would be the dimensions of such a Eurosilo.

Size of the eurosilo considered 100000 tons

No. of silos for indeginous coal 3 no.s

No. of silos for imported coal 2 no.s

Volume of one silo 100000 m3

(From experience, the bulk density of the coal is 1 T/m3 inside a 100000 m3 Eurosilo )

Dimensions of the coal silo:

Diameter of silo considered 55 m

Filling height to achieve the stockpile quantity 42.11 m

Top of silo 53.771 m

4.2 Function – transport

The coal is transported from the crusher to the Eurosilo system and from the Eurosilo system to the power plant by means of conveyors. As seen in the system layout/flow diagram, a number of conveyors in parallel streams have been considered. The reason is to satisfy the 100% redundancy requirement of the customer. Hence even if a single conveyor breaks down, the coal can be diverted through the parallel stream of conveyors to the silos. Conveyors BC-10A/B receives the material from the crusher and transports the coal to conveyors BC-11A/B which feeds on to the reversible belt conveyors, RBC-1A/B. The reversible belt conveyors could be operated simultaneously, in the required direction, to fill the indigenous and imported coal silos whenever the coal comes into the system.

The reversible conveyors either feed Silo - 2A directly or feed on to the conveyors BC-12A/B, to fill the imported coal silo – 2B.When the indigenous coal silo needs to be stored, Silo - 1A is fed directly by the reversible conveyors or the coal is fed to conveyors BC-13A/B, BC-14A/B to feed the silos – 1B, 1C.

(36)

28

The preliminary design of these conveyors have been carried out in accordance to the Indian standard IS 11592: 2000 – Selection and design of Belt Conveyors – Code of Practice.

The brief specifications of these conveyors are given below.

S.no Conveyor Length (m) Absorbed

power(kW) Motor Power (kW) Belt rating 1. BC – 10 A/B 310 541.87 600 EP 1600/5 2. BC – 11 A/B 75 122.6 160 EP 500/4 3. BC – 12 A/B 75 75.06 90 EP 500/4 4. BC – 13 A/B 75 143.31 160 EP 500/4 5. BC – 14 A/B 75 75.06 90 EP 500/4 6. BC – 15 A/B 465 227.31 250 EP 500/4 7. RBC – 1 A/B 75 55.63 75 EP 500/4

Table 4 Brief specifications of the conveyors of enclosed stockyard system

The calculations for the choice of the conveyor specifications are enclosed in Annexure - 1

4.3 Function – Stacking

The stacking and reclaiming operation is carried out by the machinery inside the silo. The silo consists of a slewing bridge supported at the centre by the roof and at the free ends, running on rails supported on the wall of the silo. The slewing action is facilitated by a slew bearing at the centre of the swiveling bridge and two drive units placed on the opposite ends of bridge.

The auger frame is suspended from the swiveling bridge and rotates as the bridge slews to reach the necessary position. The height of suspension is adjusted by means of wire ropes/cables from winches placed on the slewing bridge. The auger frame is also guided by wheels on the silo wall. This stacking function is performed by operation of a telescopic chute and the screw augers inside the silo with the aid of level sensors. Initially the coal is fed from the infeed conveyor into the silo through the telescopic chute. The screw auger is positioned at the necessary height before the coal is fed by the conveyors. The inlet chute at the discharge end of the infeed conveyor leads the coal into the telescopic chute, the lower end of which feeds the coal onto the screw augers. The coal is distributed by rotation of the screw augers towards the wall. As the coal reaches the wall, a sensor reads the situation and activates the slewing drives of the slewing bridge to rotate, thereby positioning the screw auger to distribute the coal at a different angle. The slewing stops when one layer of coal is filled and the auger is lifted to a different height to proceed with the stacking.

(37)

29

Figure 14 Eurosilo - stacking mode

4.4 Function – Reclaiming

The reclaiming operation is carried out as follows. The bottom of the silo is equipped with 2 sets of hoppers and uncoalers of redundant capacities. The uncoaler outlet is controlled by a slide valve which enables or disables the coal flow from the uncoalers. Before the start of the reclamation, the hopper and the uncoaler are filled with coal. When the uncoaler is activated to start the reclaiming operation, the coal column above the hopper is disturbed by the vibration of the uncoalers and a funnel flow cavity is formed. The slide valve is opened to feed the coal into the reclaim conveyor. As the uncoaler continues to operate, the coal level decreases in the cavity, which is monitored by a coal level sensor installed on the slewing bridge. When the coal level decreases beyond a certain level, the screw augers are activated to dig the coal and reclaim it from the silo top level and fill the cavity, so that the discharge rate is maintained.

The brief specifications of the screw auger, reclaim hopper and uncoalers are provided below.

S.no Component Qty Motor Power

(kW)

Specification

1. Screw Augers 1 132 (x2) Max. stacking capacity – 2200 TPH Max reclaiming capacity – 1100 TPH

2. Reclaim Hopper 2 - Capacity – 1100 TPH

3. Uncoalers 2 7.5 (x2) General Kinematics make

Design & comparison of open storage and closed storage system; Ontwerp en vergelijking van open en gesloten kolen opslag systemen

Specialization:

Transportation Engineering and

Logistics

Report

Number:

2016.TEL.8052

Title:

Design & comparison of open storage

and closed storage system

Author

A.E. Alangara Napoleon

Title(in Dutch):

Ontwerp en vergelijking van open en

gesloten kolen opslag systemen

Assignment:

Research

Confidential:

No

Initiator (University)

Prof. dr. ir. G. Lodewijks

Initiator (Company)

ESI Eurosilo B.V

Supervisor:

Dr. ir. D.L. Schott

Prologue

Summary

Contents

List of Figures

List of Tables

1. Introduction

2. Approach to the design process

2.1 Design Criteria

2.2 Delft systems approach

3. Preliminary design of the open stockyard system

3.1 Function – Storage

3.2 Function – transport

3.3 Function – stacking

3.4 Function – reclaiming

3.5 Function – blending

3.6 Other functions

4. Conceptual design of closed stockyard system.

4.1 Function – Storage

4.2 Function – transport

4.3 Function – Stacking

4.4 Function – Reclaiming