Energy from Waste Plants
9 November 2009, News release from Babcock Wanson UK Ltd
Solutions to Airborne Emissions from Babcock Wanson
Many new Combined Heat and Power (CHP) projects are utilising alternative fuels such as Biogas, Ethanol-rich liquids, or animal by-products such as tallow. Although these bio-derived fuels have all the right environmental credentials (non-fossil origins, renewable, lower carbon footprint, etc), their combustion is regulated by the Waste Incineration Directive (WID) regulations. These entail compliance with strict criteria for the final gaseous emissions from the exhausts of the engines used to generate electrical power. Maximum values are required on Carbon Monoxide (CO), NOx and Total Organic Carbon (TOC) plus some specified heavy metals.
Biogas normally contains relatively high amounts of Carbon Monoxide (CO) and many other organic compounds not normally found in natural gas. As a result the exhausts resulting from its combustion are high in CO and VOCs, both of which need some form of abatement before the emitted gas can be discharged to atmosphere. Other biofuels, or waste derived fuels, also contain higher amounts of organic compounds which will also usually require exhaust gas post treatment.
Thermal Oxidisers can be designed to recover heat externally (Recuperative Oxidisers) or internally (Regenerative Oxidisers). For engine exhausts the Regenerative option is usually more appropriate, but the Recuperative option can also be employed if there is sufficient local constant demand for heat energy. Careful design work can enable the exhaust pressure to help drive the oxidiser air flows, giving a substantial saving on the primary fan and its control system. The basic chemical engineering involves heating the contaminated air stream with sufficient excess air so that all the polluting contaminants are fully oxidised and suitably cleaned for direct discharge to atmosphere.
Our first project involved a 625 kWe generating set. The plant in Ravenna gives an exhaust emission of 2000 Nm3/h at 520 Deg C with high CO and VOCs. This used to be considered as outside the scope of thermal oxidation, but a successful design and installation proves that this is no longer the case.
The second project located at Bracciano was slightly larger generating 836 kWe , having to treat 3,500 Nm3/h at 510 Deg C. Another successful design was completed enabling the plant to comply with the WID on emissions.
A larger unit generating 1 MW of electricity was installed at Cicerale. This unit treats emissions from a Biogas burning engine of 4,200 Nm3/h at a temperature of 435 Deg C. The design was altered to suit the new data and another successful installation was completed.
These developments are by no means the only ones going on in thermal oxidation technology. Better ceramic media are leading to higher thermal efficiencies and lower pressure drops for reduced electrical power consumption. There are always developments to keep support fuel use as low as possible and minimise costs. Babcock Wanson is committed to this programme of continual improvement to drive the technology forward for the benefit of both customers and the environment.
For further information please email Babcock Wanson UK Ltd