The definition of Pinch Analysis
Pinch analysis is a methodology based on thermodynamic principles, that enables us to minimise the energy consumption of industrial processes by optimising the heat recovery network, energy supply levels and process operating conditions. Heat exchangers are inserted between streams that need to be cooled and streams that need to be heated. Pinch analysis allows us to estimate heat exchanger surface area requirements without knowing the heat exchanger network that will accomplish it. The analysis also indicates the thermodynamical bottleneck preventing further heat integration. The concept is also known as pinch technology, heat integration or energy integration.
The origin of Pinch Analysis
The pinch methodology emerged from systematically trying to improve heat recovery in industry through process integration. It was first introduced in a PhD-dissertation by Edward C. Hohmann in 1971. By studying processes, temperatures and entropies in a structured manner, he discovered that the heat transfer between hot and cold streams could be optimised. At the time, he couldn’t find interested parties to publish his article or steering committees willing to implement it. The main reason for this lack of interest in his theory, was that a barrel of oil only cost $ 2 back then, and implementing it would only result in very little financial benefit. With the first oil crisis in 1973, the cost of oil increased sevenfold, causing scientific institutions to try and develop optimum heat exchanger networks for maximum energy recovery. Six years later, when prices went from $ 14 to a staggering $ 40 per barrel of oil, B. Linnhoff and J.R. Flower picked up Hohmann’s theory and developed a pinch analysis tool based on thermodynamical insights.
Fig: Minimum Heating and Cooling with DTMin of 10K
The implications of the Pinch for Heat Exchanger Network (HEN) synthesis:
– No heating below the pinch
– No cooling above the pinch
– No heat transfer through the pinch
At that time already, companies understood the urge to consume less energy, to make the process more energy efficient and to look for alternative supplies.
Over time, the intuitive approach of developing a heat exchanger network resulting in the utility requirements, developed into a new and systematic procedure where the utilities and capital targets are set prior to design and the heat exchanger network is developed to satisfy the utility targets.
Today’s energy challenges in industry
The current energy market situation, unfortunately, is quite comparable to the market four decades ago. We still rely heavily on the arbitrariness of the oil and gas producing countries. Furthermore, the levels of carbon dioxide concentration are 420 ppm today, versus 315 ppm in 1960 and 280 ppm before the industrial revolution. The augmentation having been caused mainly by the growing needs for energy to meet industrial requirements. Today we know the impact of industrial growth on the environment. This has lead to a shift in focus towards reducing the impact on climate change and increasing sustainability. We are challenged to provide heat and power with the highest efficiency to preserve natural resources and the environment. This is where pinch analysis can make a big difference.
How to get started with pinch analysis
First of all, you need to get familiar with all technical details and especially with the process, by obtaining an updated process flow diagram (PFD) and a Heat & Mass Balance. This will form the basis for preparing a reliable and representative data set consisting of three components: a data set of all process streams that require heating or cooling, the design data of existing heat exchangers and finally all the information possible on heat transfer coefficients. Combining these data will allow you to make a complete analysis including the trade-off between energy and capital and feedback to the process owner. Obviously, this is not a one-man job. A pinch technician can only get all the necessary information by collaborating with at least a process owner, a maintenance engineer and a member of the engineering department.
The first analysis will indicate a pinch, which is the term for a very important temperature in the process. Above the pinch, there is a shortage of energy in the hot streams to satisfy the cold streams and below the pinch, there is excess heat. So the basic rule for an optimum network is no heating below the pinch, no cooling above the pinch, no heat transfer through the pinch. This is actually where a heat pump could be of interest: it should pick up heat where excess heat is available, which is below the pinch, and pump it up above the pinch where heat is required.
Next, the pinch technician will look for the stream that is causing the pinch and will try to alter the process slightly, in order to influence the pinch’s position. Experimenting with that pinch temperature might lead to an opportunity to achieve more integration and less energy required from outside. These tests will help determine which parts of the process need to be altered to find modifications that offer additional saving potential. Depending on the result of this final analysis, an appropriate heat exchanger network needs to be elaborated to achieve the savings calculated.
To perform an analysis for utility targeting, you can use a freeware software package. For a complete analysis including tradeoff between capital and energy, more sophisticated software is required.
In which industries and situations can pinch analysis be used?
Originally, pinch analysis was developed for the purpose of optimising utility consumption in the basic processing industry for (petro)chemicals. Very quickly, the application was extended to all industries with heat consuming processes, such as fertilisers, pulp and paper, food and beverages, pharmaceutical products, iron and steel, cement, clinkers and ceramics, etc.
The methodology is used for developing efficient, new processes and retrofitting existing plants. For an existing plant, the saving potential can be as much as 40%. The technique is also applied to optimising utility systems, making total site studies, optimising the use of process water (the water pinch) and hydrogen (the hydrogen pinch) and has even been extended to optimising manufacturing processes and personnel planning.
Success stories obtained by application of the methodology
Pinch Analysis was introduced at BASF Antwerp, Belgium in 1980. At the time, there was a boiler house with a steam capacity of 1020 t/h, supplied by 3 high pressure boilers of 220 t/h at 125 bar, 4 medium pressure boilers of 90 t/h at 20 bar, and back pressure turbines of 24 MW, 20 MW and 3 MW.
There were plans for an additional, fourth high-pressure boiler and extra 24 MW and 16 MW back pressure trubines. A pinch analysis led to the baffling conclusion that the boiler house was actually not needed at all. After implementing the identified steam-saving measures, the boiler house was completely shut down in 1985 and replaced by a backup boiler of 50 t/h.
In 1981, similar projects were initiated at the BASF site in Ludwigshafen, Germany and at all affiliates of the BASF group world-wide. As a result of the pinch analysis at the Ludwigshaven site, a coal-fired power station was shut down, the capacity of an oil-fired power station was reduced from 600 MW to 300 MW. Overall, there were steam savings of 1400 t/h, and the plans for installing 2 denox and desox plants were canceled. These results triggered the introduction of pinch technology in all major German chemical companies.
Current and future relevance
The biggest weakness of the classic pinch analysis method is that it does not appropriately consider large differences in heat transfer coefficients for various process streams. Practical applications and advanced studies have shown that optimum targets cannot be calculated when there are large differences in the heat transfer coefficients. From the analysis, a grid is derived which is used to develop the heat exchanger network. However, if that grid is incorrect or not optimised, the network can’t be optimised either. The improved method – Pinch Analysis 2.0 – takes into account those differences in the analysis stage and implements crisscross optimisation prior to design. This 2.0 approach can be applied to existing situations to further optimise the energy usage and it can make a significant contribution to meeting the EED’s energy sufficiency guidelines. According to new energy efficiency regulations, EU countries have to achieve the 20% energy efficiency target and all waste heat potential has to be defined. Pinch analysis is the only tool that can define such potential.
Daniel Declercq, PhD in Electromechanical Engineering at University of Leuven, started his career at BASF. He developed from an Energy Supply Manager (BASF Antwerp) – where he first learned about Pinch Analysis – to Project Leader Heat Integration and Energy Controller at BASF in Ludwigshafen. He continued his career as Director Energy and Hydrocarbon Feedstock Supply at Air Products Europe and as Director Business Development at Electrabel (now Engie). In 2004 he started his company Pinchco, an energy consultancy for energy efficiency and CO2 reduction in industrial processes. Daniel is also committed to promoting and further developing the pinch analysis technique. You can find more example cases, studies and helpful documents on the pinchco.com website.
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