Sustainable Energy Efficient Industrial Facility Design

Abstract

Industrial facilities are rapidly changing over the years, various technological advances have led to break-through its performance. The transformation is fetched from inventions, development of sophisticated processes/technologies, digitalization, the list is incessantly growing. These technical progressions and stratagems to realize it on the life-cycle basis forces the industries to explore sustainability concepts within the scope. Also, the mission to chop back GHG emissions to protect environment is needed than ever before. Consequently, the revolution and evolution of products, processes, technologies, resources, and sustainability requirement to mitigate climatic anomaly beams on the industrial sector and ordained it to cater an approach toward optimizing all efforts. The challenge is to develop a method by accommodating all the technological advances and sustainability requirements to transform facilities into a much better performing asset. The answer is to construct and preserve industrial facilities to be energy efficient which enable them to be competitive and environmentally friendly. The chapter illustrates, through case study, the ‘plant lifetime retrofit-ability concept in industrial facilities. Its objective is to develop the most energy efficient facility design via arranging each future modification to remain energy efficient throughout its lifecycle without deterrents and utilizing minimum capital. Finally, a way is proposed to develop inherently sustainable energy efficient design in order to cater the benefits throughout the industrial facility life-cycle.

1. Introduction

Industrial sector relies on fossil fuels as the primary source of energy that is in control of approximately one-third of world-wide energy usage. A major percentage of energy consumed is disbursed to provide utilities for oil & gas facilities in order that energy may well be engendered for other sectors. The adverse impact of fossil-fuel combustion has instigated efforts to attenuate carbon emissions, whilst environmental regulations have a considerable effect on the energy’s cost. Furthermore, it’s a competitive world with ever-increasing energy prices, industrial communities are convened to brainstorm over conservation of energy resources and profitability. Energy efficiency should be a foundational strategy to support plans to fulfill the climate policy goals moreover as for being lucrative. Energy efficiency with its integral role in energy intensive industrial processes is critically essential to realize desired energy-saving potential and reduction in Carbon Dioxide gas (CO₂₎ emissions.

The economics of industrial production, environmental conservation realities and global energy supply limitations are persistent concerns for the whole industrial sector. Regardless of where on turns, there’s an unswerving appeal to preserve energy, reduce carbon emissions, and safeguard environment for future generations. These enablers made energy efficiency as an entrenched thanks to conduct the business. In fact, energy efficiency for any industrial facility (i.e. several processes/plants tied with a central utilities-plant) is extremely dynamic and wish to be improved throughout its lifetime, nonetheless of how energy-efficient facility design was achieved during design-phase. On the opposite hand, in its entire lifetime, a plant undergoes various retrofit subjected to high-profile operational changes/improvements/profits. The changes that include process disturbances, uncertain feedstock conditions, and products demand are short-term, requiring no major retrofit. However, long-term transformations comprise of must process more raw feed, feedstock changes, improve performance etc. warrants the debottlenecking of the whole facility and comprises key retrofits. In summary, may be stated that, the retrofitting of a plant may well be needed numerous times, in its lifespan, to upgrade energy efficiency and satisfy the required increase in production rates.

The main challenge is to develop the proposed facility design into a Sustainable Energy-Efficient Design, which implies a design that’s capable of improving its energy efficiency supported by the energy-capital trade-off dynamics. Conceptually the problem will be formulated as a bi-level programming problem with two objectives, the minimum disruption within the energy utility supply (zero deficiency) and minimum energy utility consumption. In such cases the energy utility is minimized subject to least energy deficiency in supply. The outer problem of optimization of minimum energy consumption should be solved at the best-case scenario of the inner problem which is that the least possible deficiency in energy utility supply to the process plant.

On the macro level, there are three energy system components i.e. generation, distribution and utilization. Throughout the process facility design, the main target is to boost all three components of energy i.e. energy demand (process/user) minimization, efficiently fulfill energy demand (efficiently site-wide utility/supplier) and efficiently transport energy from supplier(s) to user(s). Objectives are to minimize: waste in energy, fresh resources and capital (de-bottlenecking) in these three components. This may be done via the continual upgrade of the efficiency of energy system components in generation, distribution and utilization. However, the utilization component has a unique feature, where its boundaries do not seem to be completely dictated by the process/users. Therefore, the space of improvement within this component is way wider than the others. The interaction among all three components specified waste from one component to be utilized by others and also modifications of one component supported the other components waste availability will suffice in developing energy efficient process design. Moreover, as highlighted earlier that over the last forty plus years several design standards/criteria aside from safety; health and environment besides capital and operating costs are considered, like switch-ability; flexibility; reliability; maintainability; availability; controllability; operability; acceptability and then on. Although, almost every industrial facility has to be retrofitted several times throughout its lifetime to satisfy its objectives which was coined as “retrofit with retrofit in mind approach”. “Retrofit-ability” as a design requirement has not been addressed or may be coined within the chemical engineering design community until recently. It’s worthwhile to say that the chapter emphasize to develop sustainable energy efficient design by reducing the process facility demand i.e. the utilization energy component of the process.

As an everlasting progression, sustainability may be a constantly embryonic field i.e. Every new facility that’s developed has the potential to be more sustainable and energy efficient than the preceding as new technologies and methodologies are sprouting incessantly. There are numerous ways to conserve energy throughout the planning, construction, and operation of a facility — it’s all about optimizing existing systems to further efficient settings. The expanse of energy ingesting in manufacturing has turn out to be a strategic factor in determining whether the business will remain competitive or not. There are certain rudiments of the manufacturing systems which are very difficult to alteration once the process facility is designed and meant functioning. Every manufacturing system or industrial facility design involves amassing together separate elements into a connected or a coherent whole i.e. Synthesize with the activities during which the varied process elements are combined together to generate the flowsheet of the system in order to meet certain objectives. Thus, each facility design may be a result of process synthesis which represents the configuration of the varied pieces of equipment and their interconnection represented on a flowsheet. It’s almost impossible to induce a sustainable energy efficient facility design if the definition includes process synthesis as a part of the definition, humans are always in pursuit of excellence through knowledge and it has no practical limits. New discoveries will be made and new processes are going to be synthesized to attain the identical outcomes with meager energy and capital in an exceedingly more environment friendly manner. Because the facility could not be designed to cater inventions, consequently the inclusions of it within the sustainable energy efficient facility design definition is not defensible. Hence, the definition of sustainable energy efficient facility design does not embrace process synthesis but it lies within the response of the question i.e. the way to intensify facility design for a specified process which is capable of improving its energy efficiency grounded on the energy-capital trade-off throughout its life cycle. The foremost hurdle to achieve such a design is its acceptance to “retrofit”, because the design has to be adapted several times during its life-cycle to be energy efficient. It will not be erroneous to conclude that the aspect of retrofit-ability could be a precondition for a sustainable energy efficient design [1, 2].

1.1 Retrofits

It is palpable that “Retrofits” are very significant to accomplish desired goal of developing sustainable energy efficient facility design. Retrofit/Revamp is defined as modification of a plant or facility to boost efficiency, reduce emissions and/or change capacity, and make it adequate for a replacement design or operating condition. Chemical engineering design community over the last forty plus years has considered several design criteria aside from safety; health and environment (SHE) besides capital and operating costs, like switch-ability; flexibility; reliability; maintainability; availability; controllability; operability; acceptability and then on. It’s true that any industrial facility has to be retrofitted several times during its lifetime to meet its purposes. However, “Retrofit-ability” as a design obligation has not been addressed or maybe coined within the chemical engineering design community till some recent works, it necessitates attention of the community as emissions reduction and competitiveness are sought than ever before [3, 4, 5].

There might be various objectives for a retrofit, as an example, GHG emissions reduction, utilities savings, throughput increment, modifying appropriate network topology, upgrading heat transfer units, installing additional heat transfer area, re-piping streams and re-assigning heat recovery matches etc. Pinch technology imparts a systematic technique based on thermodynamics, design and economics heuristics for saving energy in processes and on entire sites. This procedure helps optimize thermal heat recovery, and immediately became popular as a theoretically elegant yet feasible approach to scheme Heat Exchanger Networks (HENs). Heat exchanger networks (HENs) are widely applied in industrial projects over the past decades because they offer significant energy and economic savings. Applications of HEN integration is divided into two categories i.e. grassroots and retrofit design. In oil refining, retrofit design are way more common than grassroots applications. The retrofit objective is to spot an economical HEN, subject to many design and operating constraints. However, implementing aforementioned retrofit strategies in practice could also be very difficult, because of constraints associated with the topology, safety and maintenance which regularly exist during a Heat Exchanger Networks (HEN) design. Besides, the capital cost is typically high due to considerable piping and civil works required for the retrofit and potential production losses during process modification. Nowadays and since late seventies of the last century, another important frequent change is going on because of the continual escalation in energy prices at a rate that’s above plant equipment cost. It also warrants continual modification of the facility’s HEN to reinforce the plant energy efficiency along its life time (sometimes reaching up to 30 years). In such cases, the HEN retrofit objective/task is to supply a practically implementable cost-effective HEN design modification that satisfies the new process objective and its new operating constraints. There are many possible modifications for an existing HEN to retrofit the first design to the new objective. It can include a mixture of all possible process operating and design condition modifications, existing HEN topological/structural modifications, and existing HEN unit design modifications and parametric modifications (such as heat transfer enhancement to boost U) furthermore. For example, fossil oil distillation plants grassroots design including pre-heat train (PHT) is well established, but without considering Retrofit-ability criterion during the plant design phase. The design and retrofit of the crude oil pre-heat train remains to this point the topic of the many research and development work, thanks to its importance in any crude oil refinery, since the petroleum distillation system is among the biggest energy consumers within the industrial community, and also the problem is not trivial with many decision variables and constraints owed to the high interaction between the pre-heat train and also the fractionation columns of the crude distillation plant. The retrofit of the crude distillation plant including PHT may be a task that can be conducted at least 4 to 5 times along the crude oil refinery lifetime not only because of the necessity for energy saving, GHG emissions reduction but also more importantly for throughput increase. Since the atmospheric and vacuum crude distillation towers designs are highly interlinked to the crude distillation plant pre-heat train (PHT), retrofit of any one system goes to severely impact the remaining systems. All of those objectives require heat duties within the PHT to be changed, surface areas to be altered, pressure drop in the PHT is varying, the requirement for adding new heat exchangers units, the option of changing units’ sequence, the compulsion to split streams, the requisite even for new streams matching, the stipulation to change the atmospheric and/or vacuum towers internals, obligation to change crude pumps so on. Such situations will bring hard constraints to any plant owner to start out any retrofit on the idea of energy saving or energy-based GHG emissions reduction particularly, unless it’s absolutely necessary for unit de-bottlenecking via the furnace debottlenecking to permit throughput increase. In such situations usually, many good opportunities to save lots of energy consumption and reduce energy based-GHG emissions are overlooked. Although, retrofits are inevitable for nearly all facility during its lifetime but none of the facilities are designed to cater retrofits, the approach to develop facility design contains a hindrance to several improvements but especially to energy efficient modifications. Therefore, there’s dire need of assimilating retrofit-ability as a design criterion within the facility design so as to stay energy efficient through its lifecycle [1, 2].

1.2 Sustainable energy efficient facility design

Retrofits are almost inevitable for a facility to be energy efficient throughout its life-time, but it emanates with shut-down, structural (process/HEN topology) and plot-plan limitations. Altogether, these constraints make retrofit infeasible and consequently facility energy inefficient at some point in their life-time. Thus, to achieve sustainable energy efficient design a much-sought criterion is that the design that may be successfully retrofitted during the course of its life time. Retrofit-ability could be a pre-requisite criterion for the sustainable energy efficient facility design and wishes to be entrenched within the design.

A healthy-aging design supported by retrofit-ability criterion i.e. no shut-down obligation, no proposed topology alteration or no-plot plan limitations for the execution of all energy efficiency projects will be energy efficient through-out its life time. Subsequently, “Sustainable Energy Efficient Facility Design” will be demarcated as a design for a given facility which shall be capable to acclimatize any essential modification for energy efficiency (i.e. trade-off between energy cost reduction and capital investment) at any point in its life-time with none restraint owed to its existing design. The sustainable energy efficient design is capable of adjusting to the dynamic trade-off between energy cost reduction and capital investment supported the principle of energy targeting without feasibility limitations because of present design throughout its life time. It shall be developed as a design supported energy-capital trade-off changing aspects from the beginning of its life-cycle till the termination. All essential modifications shall be planned and provision is formed within the initial design to include deviations with the identical or less capital as for a brand-new design with the identical energy values.

Minimum Energy Requirement (MER) of a facility may be a subject that ride the methodology pragmatic to focus on the demand, targets among the plants may be generated supported direct/indirect integration or the other technique. Although, Pinch approach which is widely utilized in industry to get energy targets utilizes indirect targeting methodology i.e. each process has energy targets (based on direct integration) and also the integration among the processes is indirect i.e. via buffer systems like through steam headers. Direct or a mix of direct and indirect integration also called hybrid integration among different processes/plants is capable to boost energy efficiency of the facility drastically and also provide opportunities to boost facility design through plot plan optimization but has several constraints and really limited usage within the industry. Any method which might generate energy targets supported energy and capital trade-off i.e. a design criterion like global approach temperature at the beginning and end of the facility lifecycle might be utilized to develop a sustainable design from energy efficiency perspective. This criterion will define the initial design and every amendment to reach in the ultimate design such current changes offers no hindrance to the subsequent modifications. Hence, the methodology employed to attain energy efficiency within the process facility design is one among the important factors for the development of sustainable design. The methodology employed to develop energy efficiency has to be systematic. As, development of sustainable design desires to foresee energy efficient facility design supported the energy-equipment cost trade-off values for this and further. Accordingly, methods supported on impromptu energy efficiency improvement are extremely difficult to develop current design and predict future modifications to reach the final design [3, 4, 5].

2. Methodology

Process design has evolved from inventions of recent design based upon experiments to today’s novel process flow-sheet synthesis based-upon optimization. It responded to through a generation of process design based-upon the concept of stand-alone unit operations and therefor the integration between unit operations. The development of varied systematic design techniques supported on process integration has made it a promising tool in resource conservation activities. Improvement opportunities shall be identified either as process modification or design improvement as compared to the base case energy consumption regardless of the approach applied. As some approaches try to improve the energy performance of the facility design on extempore basis rather than developing it with an organized approach. Hence, it’s important to define the base case energy consumption for measuring the performance enhancement so as to gauge the advance. The section is devoted to a number of approaches together with their advantages and dis-advantages which will use to boost the energy performance [6].

2.1 Primitive approach

In primitive facility design approach (Figure 1), only core process was designed and utility was provided for all energy consumption i.e. heating, cooling or shaft work with none concept of energy efficiency or perhaps utility targeting. Consequently, the two elements were designed separately with none emphasis on energy efficiency and also the process design is directly dictating the utility system design and there aren’t any interactions among systems to boost the facility design. This approach was in practice when the efficient utilization of the resources wasn’t priority in any aspect facility design. Nowadays, the approach is sort of extinct for the mass production in process industries, can be found in practice for very small-scale production or for batch processes or processes where the production mechanism is not fully known or could not be controlled with needed accuracy.

Figure 1.

Primitive approach of facility design.

The approach is incredibly simple to implement and used generally for complex batch processes, because it is incredibly difficult to integrate them. As process and utilities systems are designed separately, only individual systems might be improved and advantages of integration cannot be realized utilizing this approach. The most advantages are simplified design and lower initial investment. There’s no element of energy efficiency from demand reduction perspective, hence obtaining a sustainable energy efficient design utilizing the approach is sort of impossible.

2.2 Conventional approach

At this time, the efficient utilization of resources and particularly of energy has become a matter of priority in many aspects of industrial and social planning. The accepted reason is that the rapid increase within the cost of key resources which has made a reappraisal of the many adopted practices necessary. Additionally, there seems to be a case for efficient resource utilization whether it would not be economically justified yet: dwindling raw materials will tend to steer further price increases - and scarcities - within the future and conservation in time will help to arrange for such a course of events. Industry was beholding to enhance for energy conservation and to reduce negative environmental impacts but there was no systematic approach to attain it within the past. The improvements were only supported by observations and lessons learned from the previous experiences, sometimes energy optimization problem was very narrowly defined to realize improvements locally which could have adverse effect at a higher level. Accordingly, the facility design approach as shown in Figure 2, is improved but only on unpremeditated basis, still no interactions were studied to boost the facility design systematically. The sole system exists was that, usually the starting design of the new facility starts with the best available existing facility design but not always. This can improve the system design for one facility supported on the previous facility design but could not predict the long run design improvements for the same as no mechanism to predict future performance with the needed design modifications.

Figure 2.

Conventional approach of facility design.

The conventional approach is predicated on the design of heat recovery system but on impromptu basis, the advantage of it’s that some energy efficiency improvements may be subsequently identified. The energy efficiency improvements are supported by experience and without considering the interaction among the systems but supported by design and operation of comparable preceding system. The approach could end in facility with better energy efficiency and straight forward to design due to segregated system but lack benefits of integration. There’s no provision within the approach to review interaction among the system to switch the system design. The approach is considered as an unstructured approach to boost energy performance without any feedback mechanism from each system. Moreover, targets supported by trade-off energy values and capital cost do not seem to be generated before the designs as a result future design performance/improvement are very tough to include into design. Consequently, improvised approach to enhance energy efficiency could not lay the inspiration of sustainable energy efficient facility design.

2.3 Pinch approach

Energy Integration is that the corner stone of process integration science. While heat recovery was the initial focus of process integration, the scope has been expanded during the late 80’s and 90’s till the end of the last century to take account of most aspects of process synthesis and design. The single most important concept and therefore the one that gave birth to the sector of process integration is that the heat recovery pinch, discovered independently by Hohmann/Lockhart, Umeda et al. and Linnhoff et al. The Pinch concept is a systematic tool that provides critical information for a complete plant or perhaps site level. The concept is additionally generally applicable in areas aside from waste heat recovery. The main target of this approach is on basic energy recovery and utility targeting, utility selection, integration of heat pumps, heat engines, furnaces, distillation columns, etc., heat exchanger network synthesis and retrofit, combined heat and power integration and process optimization for energy integration [7, 8].

2.3.1 Problem formulation

Pinch technology is the technique that provides a systematic methodology for energy saving in processes and even total sites. The methodology is predicated upon thermodynamic principles which identify economically feasible energy efficiency improvements. Pinch Analysis was first developed within the late 1970s as a method for optimization of thermal heat recovery, and rapidly gained wide acceptance as a theoretically elegant as based on first and second law of thermodynamics yet practical approach to the design of Heat Exchanger Networks (HENs). Within a short period of time, it’s evolved into a general methodology for optimization, based on the principles of process integration.

In Pinch approach, firstly, the core of every process is designed with fixed flow rates and temperatures yielding the heat and mass balance for the process. Then the design of a heat recovery system is completed for every process. Next, the remaining duties are satisfied by the use of the appropriate utilities. Process integration using pinch technology offers a completely unique approach to come up with targets for minimum energy consumption before heat recovery network design. Heat recovery and utility system constraints are then considered within the design of the core process. Interactions between the heat recovery and utility systems are also considered. The pinch design can reveal opportunities to adjust the core process to improve heat integration. The pinch approach is exclusive because it treats each process with multiple streams as a single integrated system. At site level, the waste heat is recovered using utility exchanger network i.e. utility or buffer systems are developed to recover heat from one process and utilize it for other process to attenuate net utility consumption at site level and opportunity to integrate cogeneration. It’s been applied successfully not only to energy systems (heat recovery, pressure drop recovery, power generation), but also to fresh water conservation, wastewater minimization, production capacity de-bottlenecking, and management of chemical species in complex processes.

The main advantage of the Pinch approach (shown in Figure 3) is that the designed facility is going to be very energy efficient up to the amount that systems are modified for better integration based on the interaction among them. The elements which are missing is the design retrofit-ability (i.e. future design modification as per dynamic energy prices), direct heat integration among the processes, and waste energy recovery technologies. These elements are going to be incorporated into extensions of pinch approach in future but retrofit-ability can be added to pinch approach in current format or future extensions. It’s worthwhile to mention that retrofit-ability is about provision of predicted future modifications into the current design and also the prediction might be better depending upon the approach. The elements direct heat integration and waste energy recovery technologies will affect level of energy efficiency while retrofit-ability is serving to succeed toward the extent whether high or low. Thus, retrofit-ability can be considered as a design criterion for any energy efficiency approach which is capable of predicting future designs from energy efficiency perspective. Pinch approach has all the eminence to qualify the prerequisite of an approach which might be adapted to develop sustainable design. As pinch approach may well be applied to predict the minimum energy consumption of a specified process for a given energy-capital trade-off. Henceforth, the longer-term energy consumption from the process may be predicted, supported by the energy-capital trade-off forecast. Therefore, the capital investment requirement to scale back the energy demand may well be extracted from the pinch approach and utilized to make the idea of developing sustainable energy efficient design.

Figure 3.

Pinch approach for facility design.

2.3.2 Solution methodology

For each process within the site, Pinch analysis (Linnhoff et al., 1983) are often accustomed to set the minimum energy targets through thermo-economic analysis of potential recovery and process integration, and to spot heat exchanger network design and synthesis opportunities. All processes heat flow above and below the process pinch temperature is summed up for every temperature interval to get the site sink and source profiles respectively. Transfer of heat between the site source and sink streams takes place through the utility system, the quantity of heat recovery being estimated by the overlap between the two profiles. It also links the likelihood of cogeneration within the site supported by the design of the utility system. The methodology shown in Figure 4 uses an iterative procedure to get targets for various utility system configurations and feedback among the systems. Many commercial software is accessible for heat integration within a process but only some for the site integration, none is out there for the utility synthesis. Even commercially available software has limitations in automatic design generation and would better utilized by the expert within the field [9, 10, 11].

Figure 4.

Pinch methodology to achieve energy efficient facility design.

2.3.3 Outcomes and limitations

The outcome from pinch approach may be a system that has benefits of energy recovery and in-process modifications for all processes and supplementing with energy utility system as shown in Figure 5. This approach is predicated on the economic trade-off between energy cost and equipment cost but only for a given set of values at some extent of time. The draw-back or limitation of such design is that, it does not consider the long run energy values escalation as compared to equipment cost and also future environmental regulations. These constraints are a hindrance to create the facility competitive from energy efficiency, environment or margins perspective throughout its life-cycle. All future retrofits will either require higher Capex for execution or infeasible as no provision were made within the original design for the mandatory alteration. Although, pinch design is predicated on energy values and equipment cost trade-off for the beginning of facility life-cycle but never considers the long run trade-off within the design.

Figure 5.

Facility design based on pinch approach.

One way to urge “Sustainable Energy Efficient Facility Design” is to urge sustainable design for every process within the facility which shall be modified for energy efficiency at any point in its life-time with none restraint due to its current design. A crucial feature of Pinch approach is that the ability to spot Performance Targets before the design planning is started. The ability to spot the target is the minimum requirement to appreciate sustainable design because it sets the footing of future designs and also the modifications required to attain it. The element of retrofit-ability is missing in Pinch approach but the developed design has enough flexibility (degree of freedom) to embrace this extra constraint. The approach must be extended beyond present Pinch Methodology to develop designs for all predicted trade-off values for the upcoming facility lifecycle. All the developed solutions for ever-increasing energy-capital trade-offs shall be compiled together to merge into one design which shall be modified within the future to urge subsequent designs. Finally, the availability of all identified future modifications shall be incorporated in the specified design and provisions are made for the subsequent modifications. The design developed might be modified with none hindrance at any point supported by the trade-off and could be considered as sustainable energy efficient process design. The sustainable process design approach may well be applied for each process of the facility to urge a “Sustainable Energy Efficient Facility Design”. The facility design developed with these principles has all the elements of sustainability but lacks elements which are highlighted earlier as pinch approach limitations.

Although, Pinch Methodology is incapable of developing sustainable energy efficient design but the pinch framework may be utilized to develop it. Elements which are vague in Pinch approach is retrofit-ability, process to process direct unification, and waste energy utilization technologies needs scientific community attention. In future, a framework has to be developed to handle of these limitations and take away deficiencies to develop a well-integrated energy efficient retrofit-able design which may be “Sustainable Energy Efficient Facility Design”.

3. ADU-VDU plant sustainable energy efficient design

Oil refineries are vital to the global economy and at the identical time major consumers of energy. Petroleum refineries are under increased pressure to reduce emissions of greenhouse gases, mainly CO₂ to accommodate with the upcoming stricter environmental regulations. Energy efficiency optimization may be a means solution to GHG emissions reduction because of its impact on energy consumption at the source. Heat exchangers play a significant role in crude oil refineries in energy saving, in general. Distillation is that the main consumer of energy in a crude oil refinery, and heat exchangers connected together in what’s called a preheat train are essential to dramatically reduces the thermal duty of the atmospheric crude unit furnace. Crude distillation could be a primary processing operation in refineries throughout the planet and requires heat, steam and cooling to work. Although the crude distillation unit (CDU), that consists of both atmospheric distillation unit (ADU) and also the vacuum distillation unit (VDU), is not the foremost energy-intensive plant within the petroleum refinery, in terms of energy per barrel, every barrel of oil that is processed within the petroleum refinery passes through this unit/plant, making it the most important energy consumer, of the entire energy consumed, in fossil oil refineries.

Crude distillation process separates fossil oil into fractions in keeping with boiling point so that down-streams processing units/plants are often charged with feedstock that meets their particular specifications.

Crude oil separation process is accomplished by first fractionating crude petroleum at essentially atmospheric pressure and then feeding the high-boiling fraction, called topped crude or reduced crude, from the atmospheric distillation tower bottoms to a second fractionation tower that’s operated under vacuum conditions.

The petroleum oil vacuum distillation unit is employed to avoid the high temperatures necessary to vaporize topped crude at atmospheric pressure. This unit reduces the hazard of thermal cracking, product discoloration and equipment fouling because of coke formation.

Before entering the atmospheric distillation tower flash zone, the petroleum oil charge is heated to the required desalting temperature, desalted, heated again to separate light fractions vapor during a pre-flash drum or pre-flash tower, heated again before the atmospheric unit furnace using product streams and column reflux streams, referred to as pump-arounds. The desalted and pre-flashed petroleum oil charge is heated up within the atmospheric distillation furnace(s) to about 375 C.

Topped crude from the atmospheric tower bottom sometimes called reduced crude is mixed with steam and pre-heated to about 390 C to 450 C before routed to the vacuum distillation tower. A system of vacuum pumps or steam ejectors is employed to form vacuum within the vacuum distillation column for the separation of high boiling temperatures cuts without its chemical degradation.

Crude oil distillation plants design including pre-heat train (PHT) is well established. However, the design and retrofit of the crude oil pre-heat train remains up to now the topic of many research and development because of its importance in any crude oil refinery, since the crude oil distillation system is among the largest energy consumers in industry, and therefore the problem is not trivial with many decision variables and constraints because of the high interaction between the pre-heat train and also the distillation columns of the crude distillation plant.

Nowadays, the retrofit of the crude distillation plant including PHT may be a task that may be conducted a minimum of 4 to 5 times along the fossil oil refinery lifetime not only because of the requirement for energy saving, GHG emissions reduction but also more importantly for throughput increase, change; for product mix/specification; (more gasoline than Diesel or vice versa) and permanent change in the API of the processed crude. Since the atmospheric and vacuum crude distillation towers designs are highly interlinked to the crude distillation plant pre-heat train (PHT), any retrofit of one system goes to severely impact the other. All of those objectives require heat duties within the PHT to be changed, surface areas to be changed, pressure drop in the PHT is changing, the necessity for adding new heat exchangers units, the requirement for changing units’ sequence, the necessity to streams splits, the requirement even for brand new streams matching, the requirement to alteration the atmospheric and/or vacuum towers internals, the need to change crude pumps and then on. Such situations will bring hard constraints to any plant owner to start out any retrofit on the premise of energy saving or energy-based GHG emissions reduction particularly, unless it’s absolutely necessary for unit de-bottlenecking via the furnace debottlenecking to permit throughput increase. In such situations usually, many good opportunities to avoid wasting energy consumption and reduce energy based-GHG emissions are going to be overlooked.

The feasibility of pre-heat train design modifications within the fossil oil distillation plant depends not only on the retrofit needs of the pre-heat train but also on the constraints associated with distillation towers. The interaction between the atmospheric and vacuum distillation towers, products and inter-coolers (top, middle and bottom pump-arounds) of both columns’ conditions beside its hydraulic situations create a multifarious problem to the process owners that forces them to significantly re-consider on the premise of energy saving only and/or emissions reduction any design modification especially if the desired modifications need long downtime of the plant, to be implemented. Such constraints make the choice makers of any petroleum distillation plant avoid completely any try to change the pre-heat train design and only considering the modifications which mostly accept the initial pre-heat train design with minimal changes. The petroleum refineries owners have very valid point to behave this manner.

The moves of the heat exchangers units within the crude distillation plant pre-heat train from one location to a different for re-sequencing heat exchangers units, as an example, even between the same streams, will need a crane work inside the process area and definitely a crude distillation plant down time to implement it as a project. To maneuver one heat exchanger unit within the crude distillation plant pre-heat train to a new location to be matched with another stream will even be harder not only because it needs crane work and down time but another more involved engineering project to design the new pipework required and also the pipe rack capability to accommodate the new portion of the piping system including the pre-heat train re-piping required, civil work, instrumentation and control modifications material of construction selection, safety study/HAZOP. In many situations within the crude distillation plant’s pre-heat train area, congestion will not allow such modifications in the slightest degree and if it allows it; the pipework modifications could be very expensive. Besides, in such situations the re-use of existing heat exchangers units, a minimum of from surface area point of view and/or materials of construction are going to be another unfeasible situation to contemplate for enhancing the pre-heat train energy efficiency.

Adding of new heat exchangers to reinforce the energy efficiency of the crude distillation plant pre-heat train via re-matching of streams between the crude oil cold stream and also the hot products for instance or the splitting of crude stream in one side and/or the towers products or pump around streams on the opposite side, whether or not the initial/original design may find it to be beneficial from energy saving point of view, most of the times the prevailing topology of the original design does not allow it because of the previous constraints and no way to proceed on the premise of energy saving merits alone. In many other situations the original/grassroots design of the pre-heat train does not have any merit in doing modifications to avoid wasting energy without revisiting completely the crude distillation plant pre-heat train grassroots design plot plan and re-do the design from scratch. Therefore, if we miss the “right” crude distillation plant pre-heat train grassroots design from the beginning, we are going to be constrained with the existing distillation towers and pre-heat train grassroots design plot and there’ll be very limited opportunity to boost the pre-heat train energy performance. In conclusion, the initial design cannot be improved in the least along its lifetime. Therefore, it’ll be beneficial to the petroleum refineries to form the pre-heat train design of the crude oil “right” from the beginning with inherent capability to capture waste energy with no topological modification of its original design. The inventions [US Patent 10,494,576 B2 (2019) & US Patent 10,822,551 B2 (2020)] renders energy efficient healthy aging design of crude oil refineries distillation units’ Pre-Heat Trains. The invention is related to new energy efficient configuration of integrated crude oil atmospheric and vacuum distillation units’ pre-heat train. The invention renders novel pre-heat sustainable design from energy consumption efficiency and fossil fuel-based GHG emissions’ points of view along the fossil oil refinery lifetime solely; through the pre-heat train heat exchangers’ surface areas manipulation (Figure 6). The novel pre-heat topology design is fixed and “right” from the star of the petroleum refinery commissioning up to the refinery end-of-service. It enables the cold crude oil stream of medium grade and mixed grade crude oils uses the identical topology with minimum energy consumption, compared with prior art, within the crude furnace before the atmospheric distillation column with none structural modifications along the petroleum refinery lifetime through some heat exchangers surface areas manipulation only.

Figure 6.

ADU-VDU sustainable energy efficient design.

This invention enables the crude oil refineries to know ahead of time their plot plan needs for future crude distillation units furnace debottlenecking and/or energy saving projects. The invention shown embodiment exhibits the small print of the pre-heat train’s design for the Minimum Approach Temperatures Range of 30 C to 15 C and further the thermal duties of heat exchangers (Q) in MW and temperatures in degree C (the recommended values for these designs). The energy saving compared with state-of-art brand new refineries pre-heat train configuration is up to about 30 MW of fuel saving. This saving can increase even more by up to about 50% to save up to about 50 MW of fuel using the identical invention configuration with more surface area manipulation only as mentioned above while the prior art designs do not have this capability. Taking into consideration that oil refineries can live about 50 years, the missed opportunity in both fossil fuels saving and fuel-based GHG emissions reductions are huge. Taking also into consideration that every barrel of oil going to petroleum refineries worldwide goes through this pre-heat train, the worldwide missed opportunity will be significant and increasing with time.

The developed designed shall be further developed till the end of its life-time and shall be designed for every interval of Minimum Approach Temperatures which suits normal shutdown for instance 5 C i.e. Minimum Approach Temperatures of 30 C, 25C, 20C and 15 C for a life-cycle of 20 years with a shut-down cycle of each 5 years. Because the detailed design is completed and provisions were made during the initial design, during planned shut-down exchangers areas/shell shall be installed to induced the desired energy efficiency. The design is prepared to be implemented with an awfully short cycle and might be called “off the shelves design”, as all requirements to be energy efficient supported on capital and energy values trade-off may be fulfilled with none hindrance. As ADU-VDU plant heat demand is almost constitutes of its all energy requirement, the propose design can be assumed to be sustainable energy efficient design. For a whole sustainable design all energy elements i.e. heating, cooling, shaft power and waste energy recovery technologies has to be designed in the same manner [3, 4, 5].

4. Path forward

Nowadays integration is moving away from unit operations and focuses on phenomena; like reaction, heat and mass transfer that occur within a single piece of equipment. Future systematic techniques for process integration will not only explore for integration between units but also integration within units.

Process sites produce useful products in one or more process units and use a centralized utility system to satisfy the heat and power demands of the process units. Improvements in process technology, heat recovery philosophy and enhanced throughput are a number of the various reasons why the process changes must be implemented in an exceedingly site. Because of the interactions that exist between the various subsystems (e.g. processes, heat exchanger networks and utility systems), a change in one has a knock-on effect on the other subsystems. Many of the concepts and methods developed within the past for grassroots design, operational management, retrofit and debottlenecking scenarios, have focused on utility systems and process units independently. A clear strategy and systematic approach therefore must be developed to integrate all processes and utility systems and determine the synergies among them. Developing an efficient design of energy systems (utility system) requires an honest understanding of every subsystem in compass different processes. An effective design method is one that integrates the various subsystems within the site and captures the advantages instituted on interactions between them. Another element which needs attention is that the energy available finally after all integration i.e. energy which could not be employed in the present form and will be utilized through energy recovery technologies to the form energy which is required within the site. Physical insights and graphical methods of research is accustomed to study these interactions between the various parameters within the site and estimate the impact of process changes on site targets. However, as they do not consider the prevailing constraints within the site, they are less rigorous compared to mathematical programming techniques.

The approach (Figure 7) are going to be very effective in achieving energy efficient facility design because it will unify all processes, utilities, heat recovery and waste energy utilization to come up with targets and lay the inspiration to capture direct/indirect/hybrid integration among the plants. The resultant designs are going to be optimized for the full facility as even the plot plan is going to be optimized from direct and indirect integration perspective. Moreover, the retrofit-ability aspects of the design are going to be also covered within the approach, the resultant design will not only energy efficient today but easily modified as per trade-off to stay energy efficient throughout its life cycle. Because it is extension to the Pinch approach it has all its benefits and further improvement by unifying all facility design, low-grade energy recovery and utility synthesis. It’s very difficult to magically establish such a global solution to figure from scratch. First, there should be the fundamental ingredients in situ, namely the desire of site-wide plants to participate and second proper tools and insights to conduct the analysis. These basic ingredients can then be enhanced and improved upon, with correct support structure in situ. The key to developing a successful sustainable energy efficient design is to determine the best integration among different plants and its utility system. Specifically, it’s the material and energy flows relationship among the various plants which allow establishing optimal linkage to method a fruitful inter-dynamic structure. The other element is that it also looks to the application of energy technologies to the facility which starts with the quantification of the available waste energy that will not be utilized for integration during its life-time.

Figure 7.

Approach to facility design via integrated process-recovery-utility systems.

The method should be consisting of the holistic approach for total site targeting supported on the pinch technology accompanied by mathematical programming techniques, which is that the most generally used, where it allows waste heat from processes to be used as a source of heat in other processes. The waste heat sources are converted to steam, and then passed to processes that are in an exceedingly heat deficit condition via steam system infrastructure. To spot the external heating and cooling requirements of a group of individual plants from the central utility system, the temperature/enthalpy data from individual plants are first required to be extracted from the plant after the thermal integration of its hot streams to be cooled and cold streams to be heated using individual plant’ grand composite curve. These grand composite curves define each plant’ thermal heat deficiency and thermal heat surplus after intra-plant heat integration. The collection of grand composite curves of the whole site are then accustomed graphically add all thermal deficiencies to draw the entire site heating demand curve, and add all thermal surpluses to draw the entire site cooling demand curves. Such two curves are superimposed on one graph with the present and/or suggested steam generation levels and steam supplying levels to search out the minimum total site external energy utilities requirement and naturally best indirect inter-plants thermal integration, using the site steam system. During this method, intra-integration is completed first, which implies only waste heat of one plant is shared with other plants’ members (which is not proactive form of cooperation). In this method the direct integration among adjacent plants, even using steam as a buffer, is not systematically addressed, where plant A, for example, with a surplus heat shall generate steam from its hot streams after its integration with its cold streams and send it first to the central utility and then the central utility sends it back to plant B leading to energy quality degradation and potential for mismatch between supply and demand. In this method, the mismatch within the number of steam levels required by the site users’ generation and utilization leads to energy loss with very high possibility [12, 13].

The worldwide commercial software for transitioning industrial complexes to integrated-processes-utility-energy recovery facility does not exist and even the software for planning synthesis/design of the new ones for energy efficiency optimization do not seems to be much. The current state-of-art methods focus only on indirect integration using steam, after all for obvious reasons.

In brief, a mathematical programming formulation-based software is solved successively to enumerate all possible combinations of solutions ranked from best objective function value to least for every “user-selection” type of plants’ integration (membership in an alliance to avoid wasting energy) to spot the plants for inter-plants integration and also the ones for intra-only integration together with waste energy utilization technologies as shown in Figure 8. This may give an energy efficient design for a given economic trade-off and also has capability to optimize facility plot-plan for better integration opportunities but nevertheless it must be developed to be capable of life-time retrofit-ability. This needs solutions to be generated for all future economic trade-off supported on capital and energy costs forecasts, these solutions shall be compiled together to urge a design which can be modified from initial to final design with none hindrance. Provisions shall be provided for all the longer-term future modifications within the current design to form it a “Sustainable Energy Efficient Facility Design”. The end result of the analysis is going to be highly integrated design as shown in Figure 9 which is retrofit-able throughout its lifecycle and incorporated waste energy utilization technologies.

Figure 8.

Future methodology to achieve energy efficient facility design.

Figure 9.

Future energy efficient facility design.

5. Overall summary and recommendation

5.1 Summary

The approach to attain energy efficiency in facility designed is incredibly important in achieving sustainable best-in-class energy efficient facility design. ADU-VDU case is presented to produce insight for developing plant level sustainable energy efficient design which may well be extended to the facility level. Since the facility operates as an integrated system of plants, units and streams, it must be understood in and of itself and it must be treated in and of itself. Research within the area of process systems engineering has led to a motivating breakthrough referred to as process integration. This breakthrough has expanded the influence of engineering design to methodically and insightfully address systems of multiple plants, units and streams employing a consistent basis of fundamental concepts of chemical and systems engineering. Process integration is defined as a holistic approach to design and operation that emphasizes the unity of the process. Thus, unifying all processes specified all design intents are met is that the way to achieve sustainable energy efficient design. All design aims are addressed well except Retrofit-ability, as an example Reliability, Accessibility and Maintainability is fulfilled by RAM Study while Safety and Operability requirements are accomplished by HAZOP Study. As, in its entire lifetime, an industrial facility undergoes various retrofit subjected to changes that features but not limited to process disturbances, uncertain feedstock conditions, product demand, throughput increase, feedstock changes, improve performance etc., it has to be considered as a criterion for the new design. In summary, it is stated that, the retrofitting of a plant may be needed numerous times, in its lifespan, the most effective way to approach it’s through sustainable energy efficient facility design because it will fulfill most of retrofits objectives.

5.2 Challenges

There are several challenges which hefts to be considered so as to accomplish sustainable energy efficient facility design actually, these are highlighted to lure attention from the researchers within the field;

5.2.1 Retrofit-ability as design criterion

Inclusion of retrofit-ability as a design criterion ends up in a design which will be continuously valid for whole life span of a facility and at the same time reminiscent to a new energy efficient design of the upcoming facility. Retrofit-ability insertion as a design criterion at process level up to facility level is kind of challenging because the facility designs has to be developed for all energy-capital trade-offs furthermore as other scenarios. The developed designs must be compiled together to urge a design which can be subsequently modified without hindering the old design specified as the primary design being most inexpensive and least efficient (in terms of energy consumption not energy-capital trade-off) and shall be improved with minimal capital investment throughout its life-cycle. All designs must be further developed to form provision to incorporate all identified alterations within the facility from start till end. Developing a mathematical framework to capture all elements of the sustainable energy efficient design is difficult and lack of insights; preferably it can cause to integrate processes/stream which are never studied from the unification perspective and data/information is unavailable for unifying them. The foundation of integration starts with process, which approach ascends up to facility level, leading to unifying the entire facilities process with options of direct, indirect, hybrid integration options among the processes. Consequently, springing up with sustainable energy efficient facility design is extremely difficult, even the plant level design is difficult to realize. As shown even one sustainable process design generates lots of values to the facility by improving its performances, hence, it’s advisable that in developing sustainable design evolutionary-approach may be adapted versus the more time-consuming revolutionary-approach.

5.2.2 Mathematical complexity

Analysis, like the problem definition phase, the targeting phase (approximations and heuristic rules that fail), likewise the design and optimization phase (multiple scenarios, topology traps, etc.). In theory, Mathematical Programming overcomes of these limitations however, a number of the corresponding models are extremely difficult to resolve. Moreover, the problem itself is incredibly difficult to formulate as economic trade-off predictions for the full life-cycle of a plant and develop feasible designs which might fulfill all trade-offs and provision for the inclusion of all needed modifications from start to end into a single achievable design are the parameters that cannot be easily obtained in mathematical equations. Even for a given process the insight from the prevailing design will be very difficult to formulate mathematically. If we utilize approach where all processes-utility-waste recovery are attempted to be unified which include parameters like plot plan modification’s economical evaluation etc. the formulations are tremendously difficult to obtain. This is often another excuse to focus and develop sustainable design through evolutionary-approach instead of with the more time-consuming revolutionary-approach. Finally, it should be instructive to say that Mathematical Programming could provide a framework but very difficult to urge Automatic Design, which implies that time is needed to induce solutions with experience-based directions for high-level decisions [14, 15, 16].

5.2.3 Engineering design

To transform a design into a sustainable energy efficient design, it’s important to develop conceptual designs into engineering designs which has all future modifications for implementation with none aggravations. Because the requirement is to develop facility life cycle healthy aging design, which implies it’s embedded with many designs into a single design. The necessities are to develop each design for a period and therefor the subsequent modifications afterwards, the modification must be engineered in an exceedingly way that it shall be swiftly implemented. It needs extensive design experience to capture these elements into equipment design and develop it further to other details like piping layout, foundations, plot plan etc. It needs time to conduct analysis and also due to proposed design modifications, new scenarios for several engineering activities are going to be created, as an example HAZOP or RAM Study/assessment require more times to incorporate future retrofits, which is kind of challenging to realize. Finally, to appreciate such design the foremost important equipment is heat exchanger which must be designed with better understanding about future enhancements and well flattered by other designs like piping layout, foundations etc. Available tools like 3D models would definitely help in visualizing solutions and consequently within the design development.

5.2.4 Waste energy recovery technologies

One of the challenges of Sustainable Energy Efficient Facility Design is that the application of waste energy recovery technologies, as these technologies are evolving almost each year. It’d be difficult to define the energy efficiency of the facilities because of its application, as these technologies have very different efficiencies yet as different application will ends up in very changed facility efficiencies. It’d cause the requirement of developing an expert system which incorporates all commercially available waste energy recoveries technologies and a framework for their application which is quite challenging.

6. Conclusions and recommendations

To develop sustainable energy efficient facility design evolutionary-approach shall be adapted rather than the more time-consuming revolutionary-approach. The concept is to develop sustainable energy efficient process design of every individual process, which itself is challenging but might be realized. Subsequently, once all the processes are sustainable the facility is going to be sustainable in energy efficiency develop options for inter/intra/hybrid integration together with energy recovery technologies to form the facility “best in class” from energy perspective.

Definitely obtaining a sustainable energy efficient facility design is extremely challenging but the advantages from its enormous, even a design from only heat integration perspective are great. If a design, even at a process level from heat integration perspective is produced such it’s fixed topology i.e. no new stream matches and energy efficiency improvements by area manipulation only will ends up in high energy as well as monetary savings. This is demonstrated through ADU-VDU sustainable design for a 400,000 BPD refinery, the advantages include energy savings of about $100 million NPV (depending on energy vales) together with about 90 kilo tons of CO₂ emissions reduction annually. The modification to boost energy efficiency does not require extended shut-down for energy projects but may well be drained normal shut-down window. Moreover, lesser capital expenditure is required for the design modifications as compared to retrofitting the conventional design case.

Figure 10 summarizes the benefits of Sustainable Energy Efficient Design benefits, as the solutions are “off the shelves” design i.e. pre-engineered, it does not have shut-down, structural and/or plot plan limitations. Retrofits in normal design are generally limited initially by shut-down opportunities as initially energy savings projects are feasible but later obstructed by structural limitations which implies the topology can either restricted or resulted in retrofits with very high capital and ends up with the area constrains may leads to impracticable retrofits. The constrains of shut-down, structural and plot-plan limits the facility to be energy efficient solely up to a particular level which will not able to be energy efficient supporting the economic trade-off for its life-time. On the other hand, the capital needed to do the modifications is much less in sustainable design as the provision for the modifications were made during initial design. Consequently, the initial as well as final facility design are very close to be energy efficient based on the economic trade-off. Hence, it is highly recommended for all chemical engineering community to come together for developing methods, techniques and frame-work to achieve “Sustainable Energy Efficient Plant Design” and extend it to achieve the ultimate goal of “Sustainable Energy Efficient Facility Design”.

Figure 10.

Comparison between Normal versus sustainable energy efficient design.

Nomenclature

ADU	Atmospheric Distillation Unit
BPD	Barrels Per Day
C	Degree Celsius
CDU	Crude Distillation Unit
CO2	Carbon Dioxide
GHG	Green House Gas
HAZOP	Hazard and Operability
HE	Heat Exchanger
HEN	Heat Exchanger Network
MER	Minimum Energy Requirement
MW	Mega Watt
NPV	Net Present Value
PHT	Pre-Heat Train
Q	Heat Duty of Heat Exchanger
RAM	Reliability, Availability and Maintainability
SHE	Safety Health and Environment
T&I	Turndown and Inspection
U	Overall Heat Transfer Coefficient
VDU	Vacuum Distillation Unit