How do you select the best utility system for a process network using pinch analysis?

1 What are composite curves and utility grand composite curve?

Composite curves are graphical representations of the heat sources and sinks in your process network. They show the temperature and enthalpy profiles of the hot and cold streams, and the pinch point where the minimum temperature difference occurs. The utility grand composite curve (UGCC) is derived from the composite curves by subtracting the process heat load from the utility heat load at each temperature level. The UGCC shows the net utility demand and the potential for heat recovery in your process network.

2 How to construct the composite curves and the UGCC?

In order to construct the composite curves and the UGCC, you must define the hot and cold streams and their temperature and heat duty data. This data should then be shifted by the minimum temperature difference (MTD) to account for heat transfer limitations. Plot these shifted hot and cold streams on a temperature-enthalpy diagram, starting from the lowest temperature level. After this, draw a horizontal line at each temperature level and calculate the cumulative heat load for both streams. Connecting the points of equal heat load will form the hot and cold composite curves. Finally, subtract the process heat load from the utility heat load at each temperature level to obtain the UGCC.

3 How to interpret the composite curves and the UGCC?

The composite curves and the UGCC can provide valuable insight when selecting the utility system for your process network. To determine the minimum energy requirement (MER), you can find the area under the UGCC. You can also identify the pinch point by finding the point where the hot and cold composite curves are closest to each other, and locate the optimal placement of heat exchangers by matching the hot and cold streams along the composite curves. Additionally, you can select the appropriate utility levels by finding the intersections of the UGCC with the utility supply and demand lines, and evaluate the trade-off between capital and operating costs by varying the MTD and utility levels.

4 How to select the best utility system for your process network?

In order to select the best utility system for your process network, you must consider several factors like the availability and cost of utilities (i.e. steam, hot water, cooling water, refrigerants), environmental impact and regulations, flexibility and reliability of the system (load variations, contingency plans, maintenance), as well as integration and compatibility with your process network (pressure, temperature, flow, quality). Pinch analysis can be used to compare options by calculating energy consumption, utility costs, heat recovery potential, and payback period; it can also be used to identify opportunities for improving your current system by reducing utility consumption, increasing heat recovery or modifying utility levels.

5 How to apply pinch analysis in practice?

Pinch analysis is a systematic and rigorous method for selecting the best utility system for your process network, but it also requires practical skills and experience to apply it effectively. You should be aware of the accuracy and validity of your data and assumptions, such as heat transfer coefficients and utility prices, as well as the limitations and simplifications of your models and calculations. Additionally, you should consider the sensitivity and uncertainty of your results and recommendations, such as changes in operating conditions or market fluctuations. Furthermore, consulting with other stakeholders and experts, like process engineers or vendors, will ensure that your utility system selection is aligned with project objectives, constraints, and expectations.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?