Predictive Tech Part 4: Closing the Loop

Rob Peeling, CTO at Britest, looks at energy, digital twins and the future of process industry circularity

THE PROCESS INDUSTRIES are at the heart of the global economy, providing the materials that make the goods and products from which we all benefit. However, the current linear model for exploiting the world’s resources is clearly unsustainable. We extract materials from the biosphere, damaging vital ecosystems as we go, use them once and then discard them back into the environment. It is inefficient and, given current knowledge, I would argue immoral to persist with. It is certainly the way humanity has put itself into its present predicament. The process industries need to vastly expand and develop circular management of material resources.

There is a catch however: the Second Law of Thermodynamics. Where will the energy come from to drive the processes needed to sort, concentrate and recover the materials we want for reuse? These two issues will, I believe, determine which technologies are ultimately selected for the future, and decisions will be needed within the next five to ten years.

Process electrification and energy storage

The process industries have relied on fossil fuels as their main energy source since ancient times. However, early civilisations such as the Egyptians also harnessed solar heat for simple tasks like salt production. Using hydrogen as a fuel is difficult to justify due to the significant energy required for its production (see Tom Baxter’s article on p32). It would be more efficient to use that energy directly – especially when considering safety risks and hydrogen’s relatively low specific energy density. Using hydrogen as a reductant does make sense, delivering a higher economic value. Conventional technology uses the heat of combustion of fossil fuels once, then ejects it into the environment as low-grade heat, either directly into the air or via cooling towers. Partially closing the energy loop using heat pumps makes good thermodynamic sense and a wide variety of types and capabilities are already available. With time, I expect them to become more affordable and useful over large temperature differences with perhaps a doubling of coefficients of performance.

This is, effectively, process electrification. Uptake is hindered, however, by the cost difference per kWh between fossil fuels and electricity. This is mostly a problem for policymakers in governments and industry to address. However, there is another barrier to recycling energy using heat pumps that engineers may be better placed to tackle directly, and that is timing. Pharma and fine chemicals more broadly still rely heavily on batch processing. The reasons for slow uptake of flow chemistry are better explained by human rather than technical factors and defy my word count, so let’s stick with timing. We can recover energy with a heat pump from, let’s say, a condenser in batch distillation, and it is immediately available. There is, however, no immediate demand for that energy until we run the next batch (in a simple system). There is a mismatch in time between supply and demand. Consequently, we will need new thermal battery technologies or ways of recovering low-grade heat as storable electricity. Should we revisit old ideas like organic Rankine cycles or Stirling engines?

In large-scale bulk chemical production, a shift to electric resistive heating is the obvious choice for replacing fired heaters. Not exactly a new technology but certainly one with potential new applications. There will also be niche applications for inductive heating (for electro-magnetically susceptive materials) and direct ohmic heating for some conductive process materials. For very high temperatures, arc plasmas might be useful although at present the thermal efficiency and electrode lives are a challenge. I’d particularly like to see that happen, having designed such a device 40 years ago which is still in commercial operation. More speculatively, will we see a shift in dryer designs towards radiative heating with high-power infra-red LEDs? The basic devices are already available.

Wherever the trends take us, this spread of new technology will challenge chemical engineers (and other engineering disciplines) to revise their design methods to take account of the changed heat sources.