Pinch Analysis

Minimizing energy consumption of processes with Pinch analysis

Pinch analysis is a methodology for minimizing energy consumption of processes by calculating thermodynamically feasible energy targets (or minimum energy consumption) and achieving them by optimizing heat recovery systems, energy supply methods and process operating conditions. It is also known as "process integration", "heat integration", "energy integration" or "pinch technology". Such pinch analysis results in substantial financial savings. The techniques were first developed in the early 1980’s by teams led by Professor Bodo Linnhoff at University of Manchester (UK). In France, Jean-Paul Gourlia also contributed to popularize this approach with several reference papers on this topic. Many refinements have been developed since and Pinch Analysis has been extended beyond energy applications. Pinch technology has been successfully used in a wide range of industries, including non-chemicals: food industry, paper mill, etc to improve the energy efficiency of the process and reduce the global energy bill. The method is based on thermodynamic principles and allows to determine the best heat exchangers network and utility system. It analyzes possible heat exchanges between cold streams (requiring heat) and hot streams (releasing heat) in order to minimize irreversibilities. The process data is represented as a set of energy flows, or streams, as a function of heat load (or enthalpy) against temperature. These data are combined for all the streams in the plant to give composite curves, one for all "hot streams" (releasing heat) and one for all "cold streams" (requiring heat). The point of closest approach between the hot and cold composite curves is the pinch temperature (pinch point or just pinch), and is where design is most constrained. Hence, by finding this point and starting design there, the energy targets can be achieved using heat exchangers to recover heat between hot and cold streams. In practice, during the pinch analysis, cross-pinch exchanges of heat are often found between a stream with its temperature above the pinch and one below the pinch. Removal of those exchanges by alternative matching make the process reach its energy target.

Pinch analysis can be used for existing plant retrofit as well as for new plant design. In process engineering design steps, it stands after the design of reactors and products separation equipment and prior to utility system. Main advantages of this approach includes:

• it is mainly a graphical method which allows the engineer to keep a physical approach of involved phenomenon while other optimization techniques are purely numerical;
• the energy (or exergy) minimization is performed without any knowledge of the heat exchanger network which is designed afterwards;
• a very deep knowledge of the analyzed process is not required to apply the method and retrieve substantial savings;
• it takes into account the whole process or the whole plant, providing a systematic approach instead of focusing on a specific unit or equipment;
• it is demonstrated that its use can reduce both capital and operating costs. Emissions are consequently also minimized.

Several software are available on the market to calculate the energy targets, plot the composite curves, and automatically design the heat exchanger network. Such functionalities are available in ProSimPlus software. However applying this method, in particular for existing plants improvement requires skilled and experienced engineers. It is a typical field where the engineer behind the tool is much more critical than the software itself. ProSim which starts this activity in 1992 is among the very few team which have gained such experience. For many years now, ProSim engineers perform pinch analysis, on various processes in various industries.

Reducing production costs

In many industrial sectors, energy production is the main operational cost, after the raw material. For district heating, it is the key element of an installation profitability. Ariane software purpose is to reduce and manage efficiently these production costs. In design, operations or planning phase, Ariane enables the user to determine how to best configure and operate the utilities system, at the lowest cost, according to current demands and prices.

Depending on the plant, expected savings reach several percent of the total energy bill.

Ariane is also used by many companies to evaluate the ROI of a single equipment or of an entire plant or to evaluate cogeneration agreements economic viability and performances.

A complete software to respond to all energy production issues

Ariane is a flexible and complete tool that allows the user to conduct in-depth analyses and to materialize benefits during all phases of plant life:

In design phase

• Quickly evaluate different equipment options and test new production configurations, pre-size new equipment, consider existing equipment modification ...
• Adapt an installation to norms and external constraints (in particular, those related to environmental regulation)
• Evaluate the ROI of a single investment of or a complete plant
• Evaluate the possibilities of partial resale of utilities to third parties

In operation phase

• Optimize operating parameters and determine the lowest production cost configuration
• Quickly determine the best response to unexpected event (equipment breakdown, raw material shortage...)
• Adjust the consumption of the different fuels according to the energy requirements of the network, their availability or their cost
• Evaluate and manage the level of polluting emissions and their composition (NOx, SOx, CO, Dusts...)
• Train and sensitize operators on some aspects of the plant operation

In management or planning phases

• Select the best electricity or suppliers and tariff agreement among different offers
• Evaluate the profitability of a cogeneration and the opportunity of electricity trading while knowing its exact cost
• Manage CO2 quotas, analyze costs over a long period according to load variations and resources prices
• Prepare accurate analysis of the efficiency of the plant, financial balances or budgets according to utilities produced or raw materials consumed

The full technical and economical complexity of utilities production

Thanks to a modeling environment that takes into account the full complexity of the plant and avoids simplifying assumption, Ariane allows the user to gather accurate information of the different aspects of the utilities production. Main features are :

• A full set of standards equipments (boilers, turbines, deaerators, valves...), but also specific equipment for cogeneration and district heating networks (heat exchangers, water heaters, preparators…) to represent the installation accurately
• A thermodynamic model that represent accurately the properties of water, steam and fumes
• A database that includes the most common fuel (natural gas, oil, coal…) and that the user can enrich by creating its own fuels (biomass, black liquor, wastes…).

Moreover each equipment item can be configured to take into account its technical constraints (min / max), its operating mode (run, hold, imposed or “optimizable” flow), design characteristics (yield curves…) and capital or maintenance costs. Models used are non-linear in order to allows a realistic representation of the evolution of their yield and of their enthalpy balances, which ever the load of the plant could be.

What-if studies and real-time “online” optimization

Ariane allows the user to easily create the model of a plant and to analyze “offline” different configurations or production scenarios. Plessala, an add-on module of Ariane, allows the user to run “online” optimizations that identify at regular intervals the actual operation cost, the possible minimum costs and the means to reach it. With Plessala it is possible to establish a direct link with the real-time plant database (and therefore the DCS) and to monitor Ariane to run automated calculations. Furthermore, the user can analyze, manipulate data and exploit the results in any software that supports the COM technology, in particular MS-Excel. The potential uses are then multiplied and it becomes possible to:

• Perform data validation and detect sensors failure
• Manage constraints on a long period (cogeneration contracts, annual CO2 quotas…)
• Generate retrospective balances and conduct multi-period or multi-site analyses
• Produce results according to users expectations: operators, engineers, managers…

A flexible and intuitive graphical user interface

Ariane GUI uses the most advanced MS-Windows standards and includes numerous features such as colors management, contextual windows, right click, double click, zoom…

The flowsheet drawing is done intuitively thanks to the "drag and drop" function and many additional functionalities ensure a convivial use and a fast learning:

• Drawings management (sizing, positioning, rotation, image import……),
• Units conversion tool,
• Choice of the language (English or French),
• Research module for the most complex systems,

Rigorous control on the data entered by the user has been implemented to ensure the consistency of all the parameters and to limit the number of potential mistake during conception.

Simulation results can be accessed in various ways, allowing to quickly reach the information of interest, whatever the complexity of the system. They can also be exported MS Excel format, for quick and easy dispatch.