Optimised Vacuum System Reduces Operating Costs of a Refinery
By : Editorial Team - (Spicos)

In the pursuit of energy performance , the use of optimized vacuum system in which at its peak explores a range of barriers, drivers and opportunities by improving energy performance in refining industry. Understandably, optimized vacuum system provides information to further support energy efficiency improvement efforts, which at par is energy efficiency and a cost effective means of reducing greenhouse gas emissions and energy costs, bringing additional quality and production benefits.

The process of refining crude oil to refined product can be achieved via a diverse range of refinery configurations. These configurations can be generalised into four types: simple, compound, complex and petrochemical. The simplest type consists of crude distillation, catalytic reforming and refining processes. The compound type includes the simple refinery units and units for vacuum distillation and catalytic cracking. The complex refineries have a complete slate of products including the production of lube oils. Lastly, the petrochemical type includes petrochemical plants and those which produce aromatic hydrocarbons.

 A large variety of opportunities exist to lower energy consumption. In addition to the cost saving, some projects may offer strategic advantages, whereas others may offer measureable produce and size benefits while maintaining product quality. Additionally, with marginal fuel cost increases and environmental constraints, some previously rejected energy projects may become economically viable. Nevertheless, the likelihood of nominated opportunities and the applicability of these opportunities would have to be individually assessed for a selected refinery, as each refinery is unique in its configuration and the most favourable energy efficiency opportunities will be refinery specific.

Today, vacuum technology in petroleum refineries are used to enable the purification of dense ends at low temperatures, to avoid coking and degradation of products and for other applications.

Around the globe, devices like-  steam jet ejectors and steam ejector-liquid ring vacuum pump (LRVP) combinations are the most shared methods for vacuum generation in petroleum refineries. However, due  to increasing energy costs and environmental concerns, it is essential to reduce the energy necessary for vacuum generation. It is a known fact that petroleum refineries discard a lot of waste heat to the environment, which could be used to reduce energy consumption for vacuum generation.

Usually, steam ejectors and liquid ring vacuum pump (LRVPs) combinations are generally used in petroleum refineries. It is seen that steam ejectors may have one or more phases in series or a series-parallel amalgamation, with interstage condensers, reliant on the level of vacuum necessary and the utility optimisation and operational plasticity sought for various plant loads. Considering steam ejectors being  highly reliable, and the availability of steam in petroleum refineries make these ejectors to become the natural choice.

However, they are also considered to be highly inefficient, mainly due to a lack of moving parts to convert fluid velocity to pressure efficiently. 

 The new normal in optimised vacuum system’s utilisation LRVP most commonly uses water as a seal liquid since it can be separated and reused safely. They are normally more affluent compared to steam ejectors. But widely, they do not require large heat exchangers to condense the vapour at their outlet, and the operating costs of LRVPs are generally lower than steam jet ejectors. In is not just the idea, but for better operating cost savings, a steam ejector–LRVP combination is sometimes used to replace the last one or two stages of a multistage steam ejector system. 

Usually, refining and petrochemical industries operate multifaceted energy systems based on numerous steam pressure levels, with fired boilers generating high-pressure steam and burning different fuels, and cogeneration units supplying steam and electricity to the site.

The use of diverse fuels dealing with fuel gas consumption  and production imbalances, electricity imports - exports with their equivalent commercial contracts, and lastly having to absorbed  with many environmental limitations discoursing various  economic trade-offs to operate the site-wide energy system at minimum cost.

Globally, however, there is a need for an unified approach covering all features of vacuum generation and its energy reduction possibilities. 

In several parts of the world, state of art in refineries are undertaking initiatives to deploy a site-wide energy management system (EMS) tool for assisting managers and operators in the daily decisions they need to make for management of the utilities system. That enables refineries to reduce the operating costs of its utilities system. The opportunity introduced through software model not only gives recommendations on how to optimally manage the steam and electrical network, but also calculates energy-related key performance indicators (KPI), helping to identify operational gaps and emissions of gasses.

Above all, it was established that in all-purpose, improvements can be planned and introduced in energy management by presenting routine modification, improving maintenance and adopting process control. Moreover, most notably, organisational culture change and individual behaviour change for operational excellence were found to be key steps to realising these opportunities.

It is the task that one must be aware of the fact that significant changes that brings energy efficiency improvement need capital expenditure.

The most significant barriers impeding the uptake of energy efficient technologies were firstly financial, economic and market barriers.

The refining industry worldwide faces challenges which affect industry decision making. Globally, some of the key challenges facing the refining industry have been commonly known as:  Environmental regulations,  Increasing cleanliness standards for fuels , Globalisation.

The requirement for increasing yields from crudes of decreasing quality can be achieved  by introducing adequate profit margins, by proactively dealing with public scrutiny on environmental, global warming and other issues.

Although these influences have been attributed to affect the US refining industry, they are also relevant to the refining industry worldwide. Particular regulatory and demand influences which will impact energy intensity in South African refineries moving into the future are discussed in the following section.