reverse engineering of system formmulti-stage flash distillation system integrated with solar energy

Masdar Institute of Science and Technology

ESM501 . Systems Architecture . Fall 2014

Multi-Stage Flash Distillation System Integrated with Solar Energy

Reverse Engineering of System Function

Mouza M. Al Kaabi

mmalkaabi@masdar.ac.ae

Engineering Systems and Management Masdar Institute of Science and Technology

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TABLE OF CONTENTS

1. Introduction .......................................................................................................................................... 3

2. System Context and boundry ................................................................................................................ 4

3. Function modeling of MSF and PTC systems ........................................................................................ 4

3.1. Object-Process Methodology ....................................................................................................... 5

3.2. Activity Diagrams .......................................................................................................................... 6

3.3. Design Structure Matrix ................................................................................................................ 8

4. Conclusion ............................................................................................................................................. 9

5. Refrences ............................................................................................................................................ 10

Engineering Systems and Management Masdar Institute of Science and Technology

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1. INTRODUCTION

The importance of desalination systems in the UAE was established in the previous paper

regarding system form [1], in which it was noted that the total consumption of water resources

in the Emirates today exceeds 24 times its natural recharge capacity. The water planning and

management authority is planning to cover the shortage in water supply through constructing

desalination plants. There are eight seawater desalination plants in Abu Dhabi alone, and more

are to be built since the demand for water desalination is expected to almost double in the UAE

by 2030 [2, 3, 4, 5].

However, it is necessary to improve the performance of the existing systems and provide an

enhanced design for the desalination plants that are yet to be built. The physical representation

of the form that was produced in the previous paper, illustrated the most important components

and the interfaces of the system, and presented an opportunity of retrofitting the legacy system.

This can be achieved by connecting the main heat source to the brine heater that acts as an

interface between the Multi-Stage Flash (MSF) and the renewable source of heat; the Parabolic

Trough Collectors (PTC) [1].

The aim of this paper is to:

Analyze the function of the multi-stage flash desalination system, by decomposing the processes

required to produce fresh water, while proposing a connection between the system and the

parabolic trough collectors as a renewable source for the process of water heating.

The paper therefore proceeds by presenting the details of the system context and boundary, the

function modeling of MSF systems and finally a conclusion is drawn.

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2. SYSTEM CONTEXT AND BOUNDRY

The recent economic development and rapid

population growth has caused an increase in

the demand of production of water. The

production of water and the production of

energy are coupled in the energy-water

nexus. Lubega and Farid [6] have defined the

energy-water nexus as “system-of-systems

composed of one infrastructure system with

the artifacts necessary to describe a full

energy value chain and another infrastructure system with the artifacts necessary to describe a

full water value chain.” The multi-stage flash system is extant in cogeneration plants, where

power and water are produced simultaneously. The MSF process therefore requires low pressure

heating steam which can be extracted from the power plants at low cost [7].

Figure 1 illustrates the energy-water nexus system in context of the desalination system, for

which the system boundary line is drawn around the MSF and the PTC. This paper will provide a

bottom up approach for decomposing the functions and processes in the MSF system, and

further details the process of water heating. Additionally, it traces the inputs and outputs

required to propose an enhanced system architecture that could be integrated with PTC as a

renewable heat source.

3. FUNCTION MODELING OF MSF AND PTC SYSTEMS

Representing system architecture is a dynamic procedure, where the system engineer should

consider an exchange of information between function and form to be able to develop and

improve alternative solutions [8]. Since the MSF system is an existing technology, the analysis of

this paper follows a bottom up approach, in order to simplify the functionality of the system and

decompose the main process, while tracing the inputs and outputs. The following representation

of function will be used to verify the validity of the system form previously proposed, and test if

the proposed integration with PTC is conceivable [1].

Figure 1 : System context and boundary

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3.1. Object-Process Methodology

The object-process methodology is considered a descriptive method, where the system is

represented through visual diagrams and textual descriptions. OPM can express complex and

non-linear relationships, while integrating function, structure and behavior in the same diagram.

OPM consists of three types of elements: Processes, objects and states. Directional arrows are

connecting between processes and objects to indicate procedural links. [9]

The OPM diagram shown in Figure 2 demonstrates the main process and objects constituting the

MSF and the PTC system. The process (represented by ellipse) can be divided into two main

categories; MSF related process (indicated by blue), and PTC related process (indicated by

orange). The PTC set of processes starts with the solar radiation, concentrated to heat the oil,

which subsequently acts as an instrument of heating required for MSF processes. The main input

required for the desalination process is the seawater. The seawater is transferred between

different states through the procedural links with the MSF processes, to produce the desired

output which is the fresh water.

The OPM is a useful method to illustrate the general operational view of any system, including

the entities and links in between. However, it does not provide information on the sequence of

processes, which will be demonstrated in the following sections.

Figure 2 : OPM representation of MSF and PTC processes .

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3.2. Activity Diagrams

The activity diagram, through comparisons with the OPM, provides a finer level of detail by

demonstrating the order in which the processes follow in the system. The activity diagram is used

to model the general behavior of the system, using a controlled sequence of actions to transform

inputs to outputs, and it can support continuous flow modeling, which makes it suitable to

represent the desalination system [10].

Figure 3 illustrates the flow of inputs into the two main systems; MSF and PTC. The processes

start with an initial node, while the flow takes place between inputs and outputs. The flow of sea

water can be considered an open system, where the desalination process are defined by the

required output; the fresh water. On the other hand, the PTC is a closed loop that continuously

transfers between the states of heated oil composite and cooled oil composite. The heated oil

and water exchange thermal energy in the brine heater. Since the system mainly consists of

physical process of heat and fluid transfer, these processes obey the rules of thermodynamics,

hence it is expected to have some loses in the heat energy, these loses are reduced through

added insulation to the tubes and the brine heater tank. Furthermore, the system is constructed

to produce a recovery ratio, by recycling the saline water until it reaches a high level of salinity

(>5%) where it turns to brine, it returns back to be resolved in the sea. [11]

The diagram indicates the importance of the heating process. Analyzing the function of heating

will provide further validation to the possibility of integrating a renewable heat source with the

existing MSF system, and in a cost efficient manner. Figure 4 represents an activity diagram that

provides a magnified view of the water heating process.

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Figure 3 : Activity Diagram of MSF Heated with PTC

Figure 4 : Activity Diagram of MSF Heated with PTC

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3.3. Design Structure Matrix

Design Structure matrix (DSM) is a network modeling tool, which was applied in this section to

represent and analyze the process architecture of MSF and PTC as shown in Figure 5. Some of

the advantages of representing the system in DSM are highlighting the relationships patterns

between system functions, in addition to providing a system-view that supports an optimal

decision making [12].

The connections between the processes in the matrix are indicated by different colors and each

indicates the type of interaction. Most of the connections are based on transporting the basic

fluids in the system, while the rest are based on transforming the seawater intake and the oil into

the different states, through heat exchange.

The processes of creating and transforming heat source (indicated in Figure 5 by an orange line)

is the key set of processes required to integrate the renewable energy. The MSF system will only

require retrofitting of the brine heater to adapt to the change in the heat source.

Figure 5 : DSM of MSF integrating PTC

Engineering Systems and Management Masdar Institute of Science and Technology

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4. CONCLUSION

This paper conveyed a representation of the function of multi-stage flash system, integrated with

parabolic solar collector as a low-cost, renewable source of heat used for the desalination

process. The methods used to represent the function include OPM which was used to present

the operational view of the MSF and PTC systems. These MSF and PTC systems were shown to

consist of system entities, processes and states. The activity diagram of the systems presented

the same processes with a sequence, by tracing inputs to produce the required outputs. Another

activity diagram was used to take a closer look at the heating processes that integrate the PTC

with the MSF and thus demonstrating the possibility of introducing a renewable heat source,

while maintaining the same form of the existing legacy MSF system. Finally, a DSM was used to

represent and analyze the process architecture of MSF and PTC, while indicating the types of

interactions between the functions.

It was concluded that the main set of processes that provide the potential of renewable energy

integration, is the heating process. The analysis of the functions demonstrate the possibility of

retrofitting of the form, by modifying the brine heater to receive the heat source.

The previous representations of architecture function for the MSF and PTC provide the initial

validation for integration of PTC as a heat source for the system of MSF, yet further analysis needs

to be conducted to examine the production efficiency, and the feasibility of physically connecting

the PTC to the desalination plant.

Engineering Systems and Management Masdar Institute of Science and Technology

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5. REFRENCES

[1] M. Mohammed, "Multi-Stage Flash Distillation System Integrated with Solar Energy:Reverse

Engineering of System Form," Abu Dhabi, 2014.

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EMIRATE OF ABU DHABI 2014-2018," 3 2014. [Online]. Available: http://www.ead.ae/wp-

content/uploads/2014/03/Executive-Summary-of-The-Water-Resources-Management-Strategy-

for-the-Emirate-of-Abu-Dhabi-2014-2018-Eng1.pdf. [Accessed 8 11 2014].

[3] A. Murad, H. Al Nuaimi and M. Al Hammadi, "Comprehensive Assessment of Water Resources in

the United Arab Emirates," Water Resour Manage, vol. 21, no. 1, p. 1449–1463, 2007.

[4] C. Sommariva and V. Syambabu, "Increase in water production in UAE," Desalination, vol. 138, no.

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[5] WAM, "uae interact," UAE National Media Council, 22 3 2009. [Online]. Available:

http://www.uaeinteract.com/docs/EAD_warns_against_depletion_of_Abu_Dhabis_water_resour

ces_within_next_50_years/34877.htm. [Accessed 7 11 2014].

[6] W. Lubega and A. Farid, "Quantitative engineering systems modeling and analysis of the energy–

water nexus," Applied Energy, vol. 135, p. 142–157, 2014.

[7] A. Cipollina, G. Micale and L. Rizzuti, Seawater Desalination:Conventional and Renewable Energy

Processes, Palermo: Springer, 2009.

[8] Y. Grobshtein, V. Perelman, . E. Safra and D. Dori, "Systems Modeling Languages: OPM Versus

SysML," Israel institution of Technology, Haifa, 2011.

[9] N. Soderborg, "Representing systems through object-process methodology and axiomatic design,"

11 1 2011. [Online]. Available:

http://dspace.mit.edu/bitstream/handle/1721.1/34725/50944745.pdf?sequence=1. [Accessed 18

11 2014].

[10] A. Farid, "System Architectuing: Lecture 17," Masdar Institute, Abu Dhabi, 2014.

[11] C. Sommariva, "MIT OpenCourseWare," 2 2009. [Online]. Available:

http://ocw.mit.edu/courses/mechanical-engineering/2-500-desalination-and-water-purification-

spring-2009/readings/MIT2_500s09_lec18.pdf. [Accessed 19 11 2014].

[12] S. Eppinger and T. Browning, Design Structure Matrix Methods and Applications, London: The MIT

Press, 2012.