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FEATURE MACHINE BUILDING, FRAMEWORKS & SAFETY
sponsored by Feature
developing Supercritical co2 technologieS
To make heat recovery systems appealing to users, their energy efficiency needs to be improved. Chris Horsley, process
engineering director at Babcock Wanson, discusses how the I-ThERM project set out to do this
H
igh energy prices, environmental regulations, and a desire to reduce carbon footprint, means heat recovery
is becoming increasingly popular in industry. However, with sites and processes varying, so too do the heat recovery systems. These are often bespoke or require extensive modification of existing equipment and expert installation. To truly make heat recovery appealing to users, the energy efficiency of these systems needs to be improved to reduce ROI time, and installation made far simpler. The EC Horizon 2020 grant funded I-ThERM
project, coordinated by Brunel University London, set out to do just this. The project was divided into three areas, with Babcock Wanson involved in the recovery of heat from temperatures above 300˚C using a Supercritical Carbon Dioxide System.
the development
When Carbon Dioxide is held at, or above, its critical temperature (31˚C) and critical pressure (73.8 bar), it turns into a fluid state, known as
Supercritical Carbon Dioxide (sCO2). sCO2’s thermal stability and non-flammability makes direct heat exchange from high temperature sources ranging between 350˚C - 800˚C possible. Furthermore, its physical footprint is simple and compact, and it has a low toxicity and environmental impact – all of which make it potentially appealing when it comes to heat recovery systems. However, designing and building a
The combustion chamber and burner The heater was designed for operation at up
to 780˚C air temperature with heater lockout set at 800˚C. Burner turndown ratio was retained at 5:1. The process fan size was specifically selected to account for the higher head loss associated with operation at higher working temperatures and with a heat exchanger located close to the heater outlet. A final discharge cooling system was
included, comprising of an air cooler with variable speed fan to allow the final exhaust to be cooled to around 350˚C irrespective of the heat absorbed into the sCO2.
testing the system
Babcock Wanson special MIXBLOC heater
1 DESIGN SOLUTIONS JUNE 2022 6
As the heater was being designed for a test site, we manufactured a 2m ‘dummy’ section between the combustor and cooler to allow the system to be fully commissioned and operated without the very specialist heat recovery unit being in place. This means the system can be tested at varying heat load/temperature and air flow settings without the heat recovery
Supercritical Carbon Dioxide Heater presented a host of new challenges, as not only does the heater have to contend with very high temperatures, but it would also be used for testing so needed to be adaptable. Following several briefings we built a specialist
Direct Process Air Heater, using our MIXBLOC Heater as the starting point as it is designed to provide high temperature air with no flue gas losses. MIXBLOC can operate using the process air flow as the source of combustion air, or an independent combustion air fan.
The burner & control system
unit being present to allow for the test protocol to be formalised and proved without risk to the heater battery. Both the heater and cooler unit are
manufactured in carbon steel and are fully ceramic lined to cope with the high operating temperatures. The system is natural gas fired and we also supplied a gas booster to provide up to 70 mbar of lift, plus a suitable in-line gas meter with analogue input to the MIXBLOC heater control system to display and re-transmit the gas consumption under test conditions. The final unit consisted of a fully packaged
plant complete with all controls and interfaces for both local and remote monitoring, plus remote adjustment of set parameters prewired and mounted to the heater. Control is via Siemens PLC with touch screen HMI.
the result
The resulting heat recovery technology developed by the I-ThERM project has already received significant interest across Europe from industrial organisations – especially those within the steel, cement, glass and petrochemical industries – looking to reduce their energy consumption and emissions whilst also increasing their global competitiveness. With an electrical power output of 50 kilowatt-
electric (kWe), the sCO2 system is expected to deliver energy and GHG emission savings in excess of 15% and ROI of under three years. Furthermore, the technology has been
recognised by the EC’s Innovation Radar, which identifies the most promising innovations. Professor Savvas Tassou, I-ThERM project coordinator and director of the Institute of Energy Futures, Brunel University London,
commented: “The supercritical CO2 waste heat-to-power cycle is a unique technology and the first complete system to be operational in Europe.” The project has further funding to develop
advanced heat exchanger and controls for full scale industrial sCO2 heat to power systems.
Babcock Wanson T: 020 8953 7111
www.babcock-wanson.com
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