This article on “Energy Savings in Tissue Production Process: The Case of the Hayat Tissue Mill in Turkey” by A. Isiklar, L. Aydin, D. Mainardi and O. Lopez was published in July 2008 in the TAPPSA Journal (Technical Association of the Pulp and Paper Industry of the Southern Africa). The article describes how energy can be recovered from process air in a tissue plant in Turkey using a cogeneration hood. It features three beautiful Sankey diagrams, one of which is presented here.

“The exhaust gases coming from the hood are used for the production of the steam needed to feed the YD and the other auxiliary equipment of the mill (wet strength pulper, hall ventilation). The residual energy in exhaust gases in excess from the boiler are used in order to feed a chiller unit, which in turn runs the air conditioning system of the electrical room”.

This almost symmetric top to bottom oriented diagram shows the energy in MW for a certain production capacity (details not given in the article). It is a section of the other Sankey diagram featured in the article (Fig. 3) showing the whole process including the gas turbines plant, the cogeneration hood and the waste heat boilers (omitting only the absorption chillers). Only the latter shows the reduced heat loss (see light blue arrows labeled “to atmosphere”).

As for me, that’s the kind of curves I love… 😉

Have been very busy recently and have neglected the blog. Here’s just a quick one (to get some color on the top post again … 😉 )

UK’s Department for Environment, Food and Rural Affairs (DEFRA) has crowned its new website on combined heat and power generation with a nice Sankey diagram.

What is CHP? “CHP systems are highly efficient, making use of the heat which would otherwise be wasted when generating electrical or mechanical power (…) and typically has an efficiency of over 80%”, the accompanying text explains.

The diagram is built similarly to this one presented in a previous post: The Sankey diagram doesn’t feature absolute figures, but flows are scaled in relation to the baseline of 100 units energy generation in a power plant and a CHP unit. In a cogeneration unit 160 units of energy would be produced at the same time. Losses are accounted for with 65 units in the CHP. To produce the equivalent energy quanities in a conventional power unit would cause losses 1.65 times higher than the energy output itself. In the boiler 25 % of the energy is lost (40 units).
Overall losses in convential generastion are 205 units compared to 65 units in a CHP.

Just a quick casual Friday post. Found this Sankey diagram from a Czech website in my bookmarks.

It shows that in a cogeneration unit with recovery of heat energy from engine water cooling and exhaust gas cooling, an overall efficiency of 85,4% can be achieved, and losses can be reduced to 14,6%.

Don’t ask me what the accompanying text means, I just understand that ‘Kogenerace’ is ‘cogeneration’. Note Nov 2011: I noticed that after an update the original page with the image is not available any more on

Bucknell University shows how it could reduce its GHG emissions significantly by switching over from a coal fired units to a cogeneration plant in 1998. The line-up is shown in a Sankey diagram.

Cogeneration Sankey (from Bucknell website)

Apart from the overall energy efficiency of 75% the Sankey diagram doesn’t show any figures. The shadow effects on the flows look funky, and add a spheric touch.

On my quest for more interesting Sankey diagrams I stumbled across a wykres Sankeya on a web page from Poland, which I reproduced here using ifu’s e!Sankey tool.

It shows the advantage of energy cogeneration plants over energy production in separate plants. From a base value of 100 a yield of 85% can be reached in cogeneration plants (35% electric energy, 50% heat energy – the original text accompanying the diagram says 30% electric energy, 55% heat energy) with 15% losses. To get the same energy amount from separate energy generation plants, the required energy feedstock is 1.48 times higher, with losses more than four times higher (63:15), especially originating from the generation of electricity.

While I am far from fostering one or the other technology with this post, I think this Sankey diagram merits special attention, because it is actually a 2-in-1 diagram (both with flow direction left-to-middle and right-to middle) and a baseline scenario comparison. A very nice idea!