Decarbonisation Technology - February 2022 Issue

Energy efficiency: the first step towards decarbonisation Waste heat recovery can be combinedwith a steamcycle or an Organic Rankine Cycle generator for self, continuous, and carbon-free electricity generation

Xavier d’Hubert XDH-energy

W hile industrial companies around the energy efficiency improvement and waste heat recovery (WHR) are often neglected because of a usual payback of over two years, which exceeds most companies’ rules. This is because energy efficiency and heat recovery are often considered only in terms of energy savings. When carbon dioxide (CO 2 ) reductions as a result of lower energy usage are also taken into consideration, these projects may represent the lowest hanging fruit. WHR on flue gases is a proven technology that has found a range of applications, from very high temperature electric arc furnaces (EAF) for the steel industry, or float furnaces from the glass industry to medium temperature ReHeat (RH) furnaces for steel slabs, both cement kiln and clinker coolers, to the large spectrum of low temperature streams. WHR can be combined with a steam cycle (SRC) or an Organic Rankine Cycle (ORC) generator for self, continuous, and carbon-free electricity generation or simply for warm air, hot water production and, in the near future, to warm up the feed side of solid oxide electrolyser cell (SOEC) hot electrolysers for H 2 and O 2 production. world are making bold statements about the decarbonisation of their businesses, WHR boilers have special care features that differentiate them from heat recovery steam generators (HRSGs). These include the need for a vertical gas flow arrangement for easier tube cleaning due to the high dust content in the flue gas, bare tubes made of corrosion-resistant material, and on-line cleaning systems. In this article, two WHR systems with ORC within the same plant, integrated with a thermal solar field ,will be presented. Over 7 MWe of

electricity will be generated, equivalent to over a quarter of the current electricity need of the plant. This represents a direct contribution to the decarbonisation of the industry. As these represent Capex not directed towards process improvement or production increase, financing becomes key. An example of third- party financing of energy efficiency improvement projects will also be given. The basis for such financing arrangements will be detailed, including the PPA/take-off agreement(s), solid engineering, procurement, contracting (EPC) wrap-up, bankable technology, and secure client. Importance of decarbonised electricity With all the talk around the ‘new hydrogen economy’ and CO 2 capture, utilisation, sequestration, one could lose sight of the fact that what will allow the decarbonisation of the economy is primarily decarbonised, mostly renewable electricity, be it for the transportation, heating, or industry sectors. Green hydrogen to displace grey hydrogen, heat pumps to provide low-grade heating and cooling, variable frequency drives (VFD) on motors… some of the discussions should already be settled if we want to see the emergence of standards that are necessary for the proper financing of the decarbonisation movement. Some areas remain unsettled, such as what is the best technology for energy storage, what is the best use of future captured CO 2 , mostly because there are several answers depending on a plant’s location. While direct electrification of several high temperature processes still faces some challenges, such as the clinkerisation process for a cement plant, indirect electrification can be applied almost