**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 [3–5].

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, repiping 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

*Sustainable Energy Efficient Industrial Facility Design DOI: http://dx.doi.org/10.5772/intechopen.108829*

GHG emissions reduction particularly, unless it's absolutely necessary for unit debottlenecking 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 energycapital 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 [3–5].
