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Biofuel
Verbio ’ s Nevada biomethane plant , using maize as feedstock , went online in 2021 .
Biogas plant built by Weltec : stainless-steel tank .
heating is an example of how to kill two birds with one stone : disposing of waste that would otherwise have to be incinerated or sent to landfills ( a major source of methane emissions ) while heating homes at lower cost and with fewer emissions . Other benefits include enhanced energy security and a boost to local economies . Apart from anaerobic digestion , other processes used in WtE include incineration / combustion , which produces heat for district heating or electricity ; gasification , which involves heating in a controlled , oxygen-limited environment to produce syngas ; and pyrolysis , where biomass is heated to high temperatures in an oxygen-free environment to produce gas for energy or solid and liquid materials that can be refined as bio-oil and chars . Critics of bioenergy point to the high costs and dependence on subsidies ( does bioenergy make sense when the costs of wind and solar have been plummeting ?), competition with recycling ( diversion of waste that could otherwise be recycled ), technological challenges ( many processes have been implemented only recently ) and the “ food versus
fuel ” argument , which maintains that biofuels take up land that could be used to grow food ( an objection that applies more to first-generation than later biofuels ).
Stainless steel Many of the processes used in biofuels are chemical processes , with conditions that make tough demands on materials , both in terms of corrosion and high temperatures . As in many industries , in the early days standard austenitic grades ( 304 and 316 ) were applied , but as time went on , recourse was increasingly made to duplex grades . Over time , the trend has been to replace both mild austenitics and higher grades with various duplex grades . Specifically , types 304 and 316 have been replaced by stronger lean duplex grades ( LDX 2101 was applied in many ethanol plants ); type 317 and some 6 % Mo alloys by duplex 2205 , and for some applications where 6 % Mo ( such as 904L ) and nickel alloys were applied , superduplex 2507 is now preferred for its better mechanical properties , especially in biodiesel reactor tanks . Duplex grades are now more or less obligatory in process tanks , reactor vessels and digesters . The pretreatment phases of ethanol and biodiesel plants require strong duplex grades ( 2500 and 2507 ). Weltec has recently built several biogas plants in which duplex is applied in tanks and biogas reactors . In the tanks , lean duplex type 1.4062 / 1.4162 is used in the liquid zone and superduplex 1.4462 ( 2507 ) in the gas zone . The panels are screwed together and pushed up using jacks . For the corrosive , high-pressure environment of convection syngas coolers , Alleima developed a tube where the corrosive syngas is inside the tube and the water / steam is on the outside , in Sanicro ® 30 ( UNS N08800 , EN 1.4558 ) and Sanicro ® 28 ( UNS N08028 , EN 1.4563 ).
Biogas flare in front of stainless-steel digesters . Photo : Weltec .
References
( 1 ) https :// www . iea . org / energy-system / renewables / bioenergy . ( 2 ) https :// hempking . eu / en / hemp-fuel-whatis-it ; https :// www . sciencedirect . com / science / article / abs / pii / S1364032121000794 ).
26 Heat Exchanger World February 2025 www . heat-exchanger-world . com