Pinch analysis in TH4+ design

OCTOBER 08, 2014

Based on solid thermodynamic principles and supported by intuitive graphical representations, Pinch Analysis is the tool of choice in process engineering to optimize energy integration of new and existing designs.

Our TH4+ thermal hydrolysis process has been designed from first principles following Pinch techniques. This maximizes heat recovery and results in lower operating costs.

THE PROBLEM
As illustrated by the cold composite curve (blue line) in the graph below, the thermal hydrolysis process needs to heat up the sludge from ambient temperature to about  180ºC.

Unfortunately, the available heat from the flashed vapours is only at 120ºC, as shown by the hot composite curve (red line).

In how this heat availability and demand mismatch is resolved is where the key to optimum heat integration lies.

TRADICIONAL THERMAL HYDROLYSIS SOLUTION
Like most real-life problems, this one entertains several possible solutions. The one traditionally chosen is the most simple one: part of the generated flashed steam is wasted (dotted red line) and the desired sludge temperature is achieved by means of steam generated elsewhere, at a cost.

The extent of that external steam segment (double red line) is proportional to the energy required to operate the process.

THE TH4+ solution
The TH4+ process introduces a novel, self-generated intermediate steam level, that yields two key benefits:

All internally generated steam is utilised and no steam is wasted anymore
The amount of external steam needed is minimized, and so are the energy costs.
The composite curves below  illustrate how the TH4+ process can heat the sludge up to higher temperatures (210ºC vs. 180ºC in this example) with less steam. In graphical terms, the horizontal double red line section is now shorter than before.

Interestingly, this reduced amount of steam can be generated from the anaerobic digestion biogas, making the process energy self-sufficient.

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