Removal of salt from seawater (desalination) is used to produce drinking water and water for irrigation in the Canary Islands, Spain. This is an energy intensive process.

The article ‘La importancia de los sistemas de recuperación de energía en la desalación de aguas en Canarias’ (The importance of energy recovery systems in water desalination in Canary Islands) by Baltasar Peñate Suarez and Sigrid Arenas (both of Departamento de Agua del Instituto Tecnológico de Canarias, ITC) on the IAGUA blog (in Spanish) describes how existing reverse osmosis (RO) salt removal systems with Francis turbines were retrofitted to be more energy efficient.

The two Sankey diagrams in the blog post visualize the energy flows before and after the retrofit. Energy consumption per cubic metre of water desalinated could be reduced from 3.65 kWh/m³ to 3.05 kWh/m³ by installing isobaric energy recovery devices and last generation membranes.

Check out the blog post to see both Sankey diagrams.

A Sankey diagram of O2 contamination during pressure water scrubbing from a paper on ‘Oxygen Removal during Biogas Upgrading using iron-based Adsorbents’ by Toni Raabe of DBI – Gastechnologisches Institut gGmbH Freiberg in Germany.

Flows of methane, carbon dioxide, nitrogen and oxygen are shown in vol-%. The flow rate (in m³ per hour) is given in a small table at each stage of the process chain (biomethane-process chain via pressure water scrubbing).

Here is a good example of how Sankey diagram and pie chart are used side-by-side. In fact, the Sankey diagram picks up one particular piece of information that is already in the Sankey diagram.

This is from a German research report titled ‘Entwicklung eines EnergieReduzierten Verfahrens für den Erwärmungs- und Umformungsprozess von Parabel-Lenkerfedern durch Verkürzung der Verfahrenskette („EnRed“)’ published in 2010. [Note: no English abstract present, but title translates to sth like ‘Development of an energy-reduced process for heating and forming of…’ and from what I understand it is a hot rolling process]

It compares a conventional process with a new, energy reduced process. Here is the Sankey diagram for the conventional process and the pie chart right below.

The unit is kWh/kg, primary energy per kg of final product. The three colors are picked up again in the pie chart that shows the breakdown of primary energy lost in the provision of heat (brown, 12.3%) and in the ovens (red, 74.3%). Only 13.4% of the primary energy is actually used for heating of the rolled material (yellow).

Now, the pieces of the pie chart correspond to the widths of the brown, red and yellow output arrows as part of the primary energy input at the left. We are, however, typically much more used to percentages being represented in a pie chart.

A nice detail in the Sankey diagram is the split for the three ovens and the losses from the three ovens (red). The flows run in parallel and then are joined again at a bar that reminds me of a bridge, or the nut of a guitar … or the Brandenburg gate turned sideways as my nephew suggested 😉

An interesting Sankey diagram of sugar production can be found on p. 23 and p. 24 of the 2002 report ‘Möglichkeiten der Wertschöpfungssteigerung durch Abfallvermeidung (biogener Reststoffe) und Nebenproduktnutzung – Feasibilitystudy’ by Austrian researchers Herbert G. Böchzelt, Niv Graf, Robert W. Habel, Johann Lomsek, Susanne Wagner, Hans Schnitzer (all of Joanneum Research).

Why interesting? Because the diagram wouldn’t fit on one page in the report the authors decided to cut it in two parts. Two streams of the first diagram are continued in detail in the second Sankey diagram shown on the next page.

All flows are in mass percent based on an input of 100% sugar beets (‘Rübenschnitzel’, with -schnitzel apparently meaning ‘chips’). The output of 16 mass-% ‘Presschnitzel’ (pressed beet pulp) and 4.18 mass-% ‘Melasse’ (molasses) is further detailed in the second diagram.

Mind that arrow width is different in the two diagrams, so that they two can not be compared directly. Because water dominates the first diagram, the smaller mass flows of the second diagram would be barely visible, if the two were at the same scale.

Still sitting on my hard disk are numerous Sankey diagrams I have yet to describe and post them here. The ‘Miscellaneous (Mostly) Uncommented’ series is a way to get them out to you.

A Sankey diagram from process engineering. This one is from a poster by Monika Szolucha from Warszwaw Polytechnic.

Google Translate tells me this is from a stationary membrane filter equipment that enriches methane content in biogas. Flows show throughput in kg per hour.

The scientific paper ‘A Sankey Framework for Energy and Exergy Flows’ by Kamalakannan Soundararajan, Hiang Kwee Ho, Bin Su (Energy Studies Institute, National University of Singapore) features these two Sankey diagrams.

Energy flow in an open rack vaporiser (ORV):

Exergy flow in an open rack vaporiser (ORV):

The authors explain that “ORVs regasify liquefied natural gas (LNG) from temperatures below -160°C to room temperature through a heat exchange process with sea water at room temperature and pressure. (…) The Sankey representation of energy and exergy flows here presents a large potential for energy savings that could be realised in the regasification process.”

An article on the Polish website titled ‘Rozwój biopaliw – efektywniejsze rolnictwo cz.2’ by Prof. Dr. Włodzimierz Kotowski shows the following Sankey diagram.

The process system shown is a re-esterification of rapeseed oil with methanol. Flows are mass flows shown in kilograms. Methanol is shown in blue. It is re-used and fed back into the process.

Anyone who speaks Polish who can explain further?