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.

This Sankey diagram for the water system of Segura river in Spain shows “the interchanged fluxes between the hydrological and the economical system”.

This is an output from the EU-funded ASSET (Accounting System for the SEgura river and Transfers) research project and can be found on the FutureWater website. Authored by Sergio Contreras and Johannes Hunink of Future Water (Contreras, S., J.E. Hunink. 2015. Water accounting at the basin scale: water use and supply (2000-2010) in the Segura River Basin using the SEEA framework. FutureWater Report 138).

Flows are for 2010 and measured in cubic hectometres (hm³, 1 hm³ = 1000000 m3 = 1 GL). The left part with the light blue backdrop is the actual hydric sector, while the right side with the light orange backdrop encompasses the technical/economic sector.

Water is extracted from surface waters (agua de superficie), ground water (acuiferos), and – interesting pespective – from soil water (água edáfica). Water from soil (green arrow, 901 hm³) is directly taken up by plants, so consumption is in the agricultural sector only. Agriculture is the largest consuming sector, followed by industry and energy generation, and water provision to households.

Much of the releases of water from industry and energy generation is returned to the water system (1734 hm³).

Additional tidbits of information below the Sankey diagram almost turn this into an infographic.

Interesting Sankey diagram on water use in Qingdao, China in 2011. This is from a presentation titled ‘Urban water security – Water-energy-food nexus’ by Josh Weinberg of Stockholm International Water Institute. Atkins and World Resources Institute (WRI) appear as co-authors.

Unit of flow seems to be million m³ (百万立方米). Water origin is mainly surface water (455 mio m³) and local ground water (367 mio m³), with some additional (146 mio m³) brought in from Yellow River and Yangtze River.

Not sure about the split shown with two green flows, possibly breaking down the water use to urban (city of Qingdao) and province.

The middle part shows consumers: Farming (?) is largest consumer with 311 mio m³ per year, followed by ??? with 230 mio m³, and use in industry with 153 mio m³. Polluted water is shown in black.

Maybe someone who reads Chinese wants to chime in…

Just a quick post before the weekend: Visualization of the water cycle in the Netherlands by Gunjan Singh. See initial sketch and some comments here.

Quantities are in billion kg (=million tons). “The weight of the arrows depict the proportions most of the time”, exceptions are in the thin arrows at the right which would otherwise be fine hair lines only and almost invisible.

As you are aware I am constantly looking for samples of Sankey diagrams, be they good, mediocre, or … fair.

This 2009 report on fuel cell technology (‘Natural Gas – Fueled Distributed Generation Solid Oxide Fuel Cell Systems. Projection of Performance and Cost of Electricity’ prepared by J.Thijssen LLC for US Department of Energy, National Energy Technology Laboratory, and RDS under contract number 41817M2846) has two Sankey diagrams I would like to share with you. The report assesses energy efficiency, water use and CO2 emissions of the fuel cell system.

I confess I am no expert in fuel cell technology (Wikipedia basics), and I assume the technology has evolved quite a bit over the last years. So I limit myself to a description of the Sankey diagrams presented.

On page 9 figure 3-4 shows the energy balance “Sankey Diagram of the Baseline NG DG SOFC System” (NG = natural gas, DG = distributed generation, SOFC = solid oxide fuel cell). With an energy content of the natural gas input of 9.1 MW (based on the higher heating value) and an output of 5.2 MW electric energy the system has an efficiency of 57%.
We can identify three loopbacks: syngas is recovered and fed back into the process, and heat is recovered “by thermal recuperation (by preheating the cathode air and raising and superheating steam) and chemical recuperation (by reforming part of the hydrocarbons, mainly methane, in the fuel)” (p. 8). These are the red arrows.

Now here is what I don’t like about the Sankey diagram: While most of the arrows seem to be to scale, some aren’t. Losses branching out to the top are graphically exaggerated. The arrow representing thermal losses (2.5 MW) should be about half as wide as the one for 5.2 MW ‘Net Power AC’.
The heavy spikes at the head of the arrow for inverter losses and energy used for CO2 compression overemphasize the comparatively small quantities of 0.2 MW and 0.3 MW (?!). The latter arrow seems to be labeled incorrectly (30 MW instead of 0.3 MW).

The Sankey diagram for water use of the fuel cell system on page 22 also has some obvious technical flaws:

In this diagram we are looking at water flow rates in kg/s. It seems as if most of the water is in a closed loop (0.52 kg/s) in the syngas recovery. The report on page 21 explains that “[w]hile the water demand for the NGDG system is considerable, net water use for the NGDG system is minor (only about 0.15 gal/kWh or 790 gal/day […]). The steam reformer has a steam demand more than 10 times this amount (about 0.55 kg/s)”. The label of the feed arrow at the top left has a wrong label and refers to 790 gal/hour(!).

The magnitude (width of arrow) of the main loop representing a flow rate of 0.52 kg/s water in syngas recycle is not maintained especially in the curves.
The main problem however is that it is not clear at which process step water comes in or flows out. I have come to the conclusion that the arrows for inflows (increase of arrow width) and outflows/losses (decrease of arrow width) are actually missing. So if you imagine an outward arrow to the label “0.12 kg/s water consumption at SMR” and two inward arrows from “0.44 kg/s water production in stack” and “0.06 kg/s water production in burner” the Sankey diagram starts to make sense.

Will try to draw my own version of the Sankey diagram and present it here. Note that ‘SMR’ is for steam methane reforming, abbreviation not explained in the report.

This presentation on ‘Water Management for Fossil Energy Systems’ by Susan M. Maley, Technology Manager for Crosscutting Research at the U.S. Department of Energy (DOE) / National Energy Technology Laboratory (NETL) gives an overview of the activities and research into ‘Current Activities in Water Management Research and Development’.

On page 9 it features these two Sankey digrams showing water usage in a 500 MW pulverized coal plant.

On the left the situation without CO2 capture, on the right with CO2 capture. Water withdrawal almost doubles (524 gal/MWh to 1049 gal/MWh) when implementing CO2 capture.

Mind that the left and the right Sankey diagram can not be compared directly as they use a different scaling factor.

Via the EDF blog (no, not Electiricité de France, but Environmental Defence Fund) comes this mixed Sankey diagram for energy and water flows in the U.S. in 2011.

Kate Zerrener explains in the post that energy generation and water consumption are deeply interwoven. The diagram shows which energy production and which consuming sector requires how much water.

“Water is measured in billions of gallons per day (BGD) and energy is measured in quadrillion British Thermal Units (Quads) per year. In the graphic above, water flows are represented in blue, energy in green.”

I have talked about a cereals Sankey diagram by INRIA Grenoble a couple of weeks ago in this post.

Here are two more Sankey diagrams from the underlying article ‘Etude des flux de céréales à l’echelle locale: Exemples en Rhône-Alpes, en Isère et dans le SCOT de Grenoble’ by J. Courtonne, J. Alapetite, P. Longaretti, D. Dupré.

These are the mass flows for cereals production in France (2007/2008) in Mt (1000 tons)

Here is the same cereals process chain “translated” into a water footprint. Unit is million cubic metres of water consumed.

A very clear structure in both diagrams with three columns: grains production, transformation and final products. Choice of color corresponds to the topic.