Apr-2015

Best practice in energy efficiency

Energy management software tools provide solutions for energy savings from design through operation

Ron Beck
AspenTech

Article Summary

Energy management is essential to the sustainability and profitability of an operation. Second to raw materials, energy is the largest expense in most chemical and refining processes. Those refineries and petrochemical companies that invest in energy efficiency gain a competitive advantage through improved operating margins, production flexibility and better carbon footprints. Improving energy consumption should be seen as a business opportunity and embedded within all aspects of the enterprise. External and internal factors make energy optimisation an on-going challenge in any operation. Energy sources, supply and costs are changing and evolving. Feedstock shifts impose adjustments in operating strategies. Sales contracts impose constraints. Environmental regulations and taxes can force operating shifts whilst equipment ages with time and its condition impacts operating effectiveness (for instance, heat exchangers age and get fouled).

So, how can refiners and petrochemicals companies keep energy efficiency foremost in mind in the midst of business complexity and uncertainty? 

Tackling energy inefficiency is divided into supply-side and demand-side areas. On the demand side, there are various strategies for reducing energy demand. Fundamentally, making more efficient use of all heating and cooling sources presents opportunities in a plant. This is known as heat integration and is tackled during design, but also on any operating facility. Demand can be reduced through better operation and maintenance of process equipment. Heat exchangers encounter a variety of operating challenges ranging from fouling on heat transfer surfaces, vibration and hydraulic issues. Process strategies can have a significant impact on energy use – for instance, adjusting operating temperatures, tuning and adjusting column tray and flow. Reducing process variability (through optimisation and real time control) can significantly improve efficiency. On the supply side, actively managing the available utility sources based on their temporal pricing and supply typically can achieve enormous savings.  

In summary, there are four strategic opportunity areas for energy savings:
•    Better design of new facilities
•    Capital investment to revamp processes for energy efficiency
•    Improvement in operating and maintenance strategies
•    Effective management of utilities for either lowest cost or lowest energy use.

It is a combination of these four elements that the refining industry needs to undertake to respond effectively to the issues in energy efficiency and carbon footprint.

Design for energy efficiency
Process engineering design faces a range of design objectives, starting with yield and quality targets, feedstocks, flexibility to handle changes in feedstock and product over time, safety and emissions compliance, operating stability and capital cost minimisation. When energy efficiency is relegated down the priority list there will be a negative impact over the life of the plant.

The enemy of energy efficient designs is time. Most projects today, whether large or small, are under huge pressure with regard to schedule. The most proven or easiest to design process (from a functional point of view) gets developed. Incorporating heat integration (pinch) analysis into this early stage can yield important lifecycle benefits. Energy efficient processes not only save lifecycle costs, but also capital through reduction in required ratings. This will help also to save hot and cold utilities.

Ways to improve energy optimisation at the early design stage include:
• Intuitive heat integration (pinch) analysis and optimisation software embedded within the process simulation enables the conceptual designer to rapidly investigate, screen and select better designs from an energy point of view
• Detailed heat exchanger modelling within the process simulation enables the conceptual designer to look at trade-offs between heat exchanger size, efficiency and operability to achieve the best balance of capital and operating cost
• Optimisation of the interaction between heating and cooling block and key process units, such as separation columns, using optimisation methods within leading process simulators such as Aspen Plus and Aspen Hysys.

Energy conservation is important, not only to large petrochemical processes, but also to new bio-conversion processes seeking commercial viability. Liquid Light1 is a start-up company which is commercialising patented bio-to-chemicals processes and Pan Pacific2 is a company addressing conceptual process design of algal biofuels production. Both organisations have made use of these early design approaches to improve the economics of their novel processes. Braskem has developed an innovative energy efficient process for synthesising isopropanol from sugarcane by utilising the above approach. Some 30% energy saving is achieved in the early stage of process design with the right combination of process knowledge and software tools like energy analysis inside Aspen Plus.⁸

Revamping existing facilities
Diverse opportunities are available to improve energy use in existing facilities and many of these alternatives fortuitously improve yields. The same tools, which are available during front end design, are similarly available to the engineer looking at energy conservation and plant improvement. Several of the key opportunity areas are reconfiguration of heat exchangers; replacement and addition of heat exchangers; more aggressive preventative maintenance strategies to reduce heat exchanger fouling; process changes in operating parameters and configuration to improve efficiency.

A comprehensive energy analysis of an existing process facility may identify dozens of individual opportunities for improvement, some of which involve significant capital expense and others that involve trade-offs in production, achieving both energy reduction and yield improvement. LG Chem, in a recently published case, gained both energy savings and a 10% yield improvement through column integration and better process sequencing.³ 

Operations and maintenance strategies
A range of operating practices and strategies are available to improve collectively the energy use within a plant. Several of these include:
•    Visibility of energy use KPIs

Visual key performance indicator (KPI) dashboards representing plant performance are the starting point for operational improvement. When all operators, maintenance personnel, planners and managers understand the impact of their actions on plant energy use and costs, it gives each individual in an operating environment ownership of the energy challenge.